U.S. patent number 9,883,262 [Application Number 14/407,716] was granted by the patent office on 2018-01-30 for optical network system, optical switch node, master node, and node.
This patent grant is currently assigned to NIPPON TELEGRAPH AND TELEPHONE CORPORATION. The grantee listed for this patent is NIPPON TELEGRAPH AND TELEPHONE CORPORATION. Invention is credited to Kyota Hattori, Masaru Katayama, Naoki Kimishima, Akira Misawa, Masahiro Nakagawa.
United States Patent |
9,883,262 |
Hattori , et al. |
January 30, 2018 |
Optical network system, optical switch node, master node, and
node
Abstract
An optical network system includes a master node and a plurality
of optical switch nodes, allowing the number of nodes without
depending on the number of wavelengths. The master node is
configured to: divide a wavelength path having an arbitrary
wavelength into time slots each having a predetermined time period;
and allocate the time slots to each of the optical switch nodes.
Each of the optical switch nodes is configured to: synchronize the
time slots based on information delivered from the master node; and
thereby transmit or receive a data or performs route switching.
Inventors: |
Hattori; Kyota (Musashino,
JP), Kimishima; Naoki (Musashino, JP),
Nakagawa; Masahiro (Musashino, JP), Katayama;
Masaru (Musashino, JP), Misawa; Akira (Musashino,
JP) |
Applicant: |
Name |
City |
State |
Country |
Type |
NIPPON TELEGRAPH AND TELEPHONE CORPORATION |
Chiyoda-ku, Tokyo |
N/A |
JP |
|
|
Assignee: |
NIPPON TELEGRAPH AND TELEPHONE
CORPORATION (Tokyo, JP)
|
Family
ID: |
49758292 |
Appl.
No.: |
14/407,716 |
Filed: |
June 13, 2013 |
PCT
Filed: |
June 13, 2013 |
PCT No.: |
PCT/JP2013/066350 |
371(c)(1),(2),(4) Date: |
December 12, 2014 |
PCT
Pub. No.: |
WO2013/187474 |
PCT
Pub. Date: |
December 19, 2013 |
Prior Publication Data
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|
|
Document
Identifier |
Publication Date |
|
US 20150131991 A1 |
May 14, 2015 |
|
Foreign Application Priority Data
|
|
|
|
|
Jun 13, 2012 [JP] |
|
|
2012-133775 |
Jun 13, 2012 [JP] |
|
|
2012-133776 |
Feb 21, 2013 [JP] |
|
|
2013-032134 |
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H04Q
11/0005 (20130101); H04J 14/0286 (20130101); H04J
14/0257 (20130101); H04J 14/0212 (20130101); H04J
14/0267 (20130101); H04J 3/085 (20130101); H04J
3/0655 (20130101); H04J 14/08 (20130101); H04Q
2011/005 (20130101); H04Q 2011/0045 (20130101); H04Q
2011/0086 (20130101); H04J 14/0283 (20130101); H04J
14/0284 (20130101); H04Q 2213/1301 (20130101); H04Q
2011/0033 (20130101) |
Current International
Class: |
H04J
14/00 (20060101); H04J 3/06 (20060101); H04J
3/08 (20060101); H04J 14/08 (20060101); H04J
14/02 (20060101); H04Q 11/00 (20060101) |
Field of
Search: |
;398/47,45,51,54 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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|
|
|
|
|
101953098 |
|
Jan 2011 |
|
CN |
|
1395067 |
|
Mar 2004 |
|
EP |
|
H11-313067 |
|
Nov 1999 |
|
JP |
|
2002-158615 |
|
May 2002 |
|
JP |
|
2002-237824 |
|
Aug 2002 |
|
JP |
|
WO 03/084109 |
|
Mar 2003 |
|
WO |
|
Other References
Office Action for Japanese Patent Application No. 2014-521404
(dated Sep. 8, 2015). cited by applicant .
Office Action for Chinese Patent Application No. 201380031284.4
(dated Jan. 17, 2017). cited by applicant .
International Search Report for International Application No.
PCT/JP2012/066350 dated Jul. 16, 2013 (4 pages). cited by applicant
.
Kazuo et al. "Introduction to Optical Network Becoming More
Familiar (15), ROADM that can freely operate an optical core
network." Nikkei Business Publications, Inc. Jun. 15, 2006 (4
pages). cited by applicant .
Chiaroni et al. "Demonstration of Interconnection of Two Optical
Packet Rings with a Hybrid Optoelectronic Packet Router. "
Alcatel-Lucent Bell Labs, France. (3 pages). cited by applicant
.
Extended Search Report for European Patent Application No.
13803547.2, dated May 3, 2016. cited by applicant .
Search Report for European Patent Application No. 17185579.4 (dated
Nov. 29, 2017). cited by applicant.
|
Primary Examiner: Sedighian; M. R.
Attorney, Agent or Firm: Merchant & Gould P.C.
Claims
The invention claimed is:
1. An optical network system, comprising: a master node; and a
plurality of optical switch nodes, wherein the master node is
configured to divide a wavelength path having an arbitrary
wavelength into time slots each having a prescribed time period,
allocate the time slots to each of the optical switch nodes,
deliver a control signal including a time slot start time and a
time stamp to each of the optical switch nodes, and wherein, upon
receipt of the control signal from the master node, each of the
optical switch nodes is configured to synchronize the time slots,
based on a time common to all of the optical switch nodes, the
common time being determined by setting a time shifted by a
propagation delay time, and thereby transmit or receive a data or
perform route switching.
2. The optical network system according to claim 1, wherein each of
the optical switch nodes is configured to synchronize the time slot
based on a trigger delivered from the master node.
3. The optical network system according to claim 2, wherein the
trigger contains therein time slot information showing instruction
contents on data processing.
4. The optical network system according to claim 1, wherein the
master node is configured to deliver time slot information showing
instruction contents on data processing, to each of the optical
switch nodes.
5. The optical network system according to claim 1, wherein the
master node is configured to deliver a control signal including a
time slot start time and a time stamp to each of the optical switch
nodes, and wherein each of the optical switch nodes is configured
to: share information on a common time; upon receipt of the control
signal from the master node, synchronize the time slots, based on a
delay time obtained by subtracting a value of a time stamp from a
receipt time of the control signal; and thereby transmit or receive
a data or performs route switching.
6. The optical network system according to claim 1, further
comprising a ring optical network that performs optical
transmission by means of wavelength multiplexing, wherein each of
the optical switch nodes is provided in the optical network, and is
configured to perform an optical switch operation and insertion and
branching of a data, and wherein the master node is configured to:
allocate time slots to each of the optical switch nodes such that
collision of data does not occur in the optical network; deliver
time slot information showing the allocated time slots to each of
the optical switch nodes; and perform a bandwidth allocation by
reallocating the time slots according to traffic volumes between
the optical switch nodes.
7. The optical network system according to claim 6, wherein the
master node is provided in one of a plurality of the optical switch
nodes.
8. The optical network system according to claim 6, wherein the
master node comprises: a traffic information collection unit that
is configured to collect traffic information transmitted from each
of the optical switch nodes; a time slot allocation unit that is
configured to allocate a time slot to each of the optical switch
nodes using the collected traffic information; and a time slot
delivery unit that is configured to deliver the time slot
information, and wherein the optical switch node comprises: an
optical time slot switching unit that is configured to perform an
optical switch operation and insertion and branching of a data; a
time slot transmit-receive unit that is configured to transmit or
receive a data between an external communication device connected
to the optical switch node and the optical time slot switching
unit; and a time slot synchronization unit that is configured to
control the optical switch operation at the optical time slot
switching unit and timing of the data transmission and reception at
the time slot transmit-receive unit, based on the time slot
information delivered to the optical switch node.
9. The optical network system according to claim 8, wherein the
master node: further comprises a time slot start delivery unit that
is configured to generate a trigger indicating a start of a time
slot at prescribed periods; and deliver the time slot information
and the trigger on the same path, and wherein the time slot
synchronization unit of the optical switch node is configured to
provide control on the optical time slot switching unit and the
time slot transmit-receive unit such that the trigger received by
the optical switch node is detected, and, based on the trigger, a
processing specified by the time slot information is performed.
10. The optical network system according to claim 9, wherein, in
the optical network, the trigger is transmitted using a wavelength
for control in the optical network or using a fiber which is
different from that used for data transmission between the optical
switch nodes.
11. The optical network system according to claim 6, wherein a time
length of the time slot or a repetition period of the time slot is
set at one over the integers of a propagation delay for one round
of the optical network.
12. The optical network system according to claim 8, wherein the
time slot information includes information on a start time of a
time slot, and wherein each of the optical switch nodes is
configured to perform a processing specified by the time slot
information in accordance with the start time, based on a local
time of the optical switch node.
13. The optical network system according to claim 12, wherein the
master node further comprises a time delivery unit that is
configured to deliver a time synchronization frame which has a
local time of the master node as a time stamp, to the optical
switch node, and wherein, upon receipt of the time synchronization
frame, each of the optical switch nodes is configured to set a
local time of its own at a time indicated by the time stamp.
14. The optical network system according to claim 13, wherein, in
the optical network, the time synchronization frame is transmitted
using a wavelength for control in the optical network or using a
fiber which is different from that used for a data transmission
between the optical switch nodes.
15. The optical network system according to claim 12, wherein a
common time independent of a propagation delay is set to each of
the master node and the optical switch nodes, as a local time, and
wherein the master node is configured to allocate the time slots
based on a measurement result of a propagation delay time of each
of the optical switch nodes, such that data collision does not
occur.
16. The optical network system according to claim 8, wherein a time
length of the time slot or a repetition period of the time slot is
set at one over the integers of a propagation delay for one round
of the optical network.
17. The optical network system according to claim 9, wherein a time
length of the time slot or a repetition period of the time slot is
set at one over the integers of a propagation delay for one round
of the optical network.
18. The optical network system according to claim 10, wherein a
time length of the time slot or a repetition period of the time
slot is set at one over the integers of a propagation delay for one
round of the optical network.
19. The optical network system according to claim 1, comprising a
single ring network comprising a single ring, or a multi-ring
network in which a plurality of rings are connected in multiple
stages, wherein one of the nodes on the ring is a master node,
wherein the master node is configured to set a time of each of the
nodes other than the master node as an optical switch node, wherein
each of the nodes other than the master node is configured to tick
a first time slot starting from a time set by the master node,
wherein, based on a propagation delay time between the master node
and each of the nodes other than the master node and on a
propagation delay time for one round on the ring, the master node
is configured to calculate an offset value of a specific node which
is specified from among the nodes other than the master node and
set the calculated offset value to the specific node, and wherein
the specific node is configured to tick a second time slot which is
a time slot having a start timing shifted from a start timing of
the first time slot of its own node by the offset value set by the
master node.
20. The optical network system according to claim 19, wherein the
master node is configured to transmit a synchronization frame to
which a current time inside the master node is given as a time
stamp, to each of the nodes other than the master node, wherein
each of the nodes other than the master node is configured to: set,
upon receipt of the synchronization frame, the time stamp in the
synchronization frame as a current time inside its own node; and
transmit a delay measurement frame to which the current time inside
its own node as a time stamp, to the master node, and wherein the
master node is configured to measure, upon receipt of the delay
measurement frame, a propagation delay time between the master node
itself and each of the nodes other than the master node, based on
the time stamp in the delay measurement frame and on the current
time inside the master node itself.
21. The optical network system according to claim 20, comprising
the single ring network, wherein the master node is configured to:
transmit a synchronization frame to the master node itself; and
measure, upon receipt of the synchronization frame, a propagation
delay time for one round on the ring, based on a time stamp in the
synchronization frame and on a current time inside the master node
itself.
22. The optical network system according to claim 21, wherein the
master node is configured to determine an offset value to be set to
the specific node, based on a result of the measurement of the
propagation delay time between the master node and each of the
nodes other than master node and on a result of the measurement of
the propagation delay time for one round on the ring, also taking
into account a direction of a time slot and presence or absence of
a jump over the master node.
23. The optical network system according to claim 6, wherein the
time slot information includes information on a start time of a
time slot, and wherein each of the optical switch nodes is
configured to perform a processing specified by the time slot
information in accordance with the start time, based on a local
time of the optical switch node.
24. The optical network system according to claim 23, wherein the
master node further comprises a time delivery unit that is
configured to deliver a time synchronization frame which has a
local time of the master node as a time stamp, to the optical
switch node, and wherein, upon receipt of the time synchronization
frame, each of the optical switch nodes is configured to set a
local time of its own at a time indicated by the time stamp.
25. The optical network system according to claim 24, wherein, in
the optical network, the time synchronization frame is transmitted
using a wavelength for control in the optical network or using a
fiber which is different from that used for a data transmission
between the optical switch nodes.
26. The optical network system according to claim 23, wherein a
common time independent of a propagation delay is set to each of
the master node and the optical switch nodes, as a local time, and
wherein the master node is configured to allocate the time slots
based on a measurement result of a propagation delay time of each
of the optical switch nodes, such that data collision does not
occur.
27. The optical network system according to claim 20, wherein the
multi-ring network comprises an upper ring and a lower ring which
are connected by a ring intersection point node, and the master
node is located on the upper ring, wherein the master node is
configured to: transmit a synchronization frame to the master node
itself; and measure, upon receipt of the synchronization frame, a
propagation delay time for one round on the upper ring, based on a
time stamp in the synchronization frame and on a current time
inside the master node, and wherein the ring intersection point
node is configured to: transmit a synchronization frame to the ring
intersection point node itself; and measure, upon receipt of the
synchronization frame, a propagation delay time for one round on
the lower ring, based on a time stamp in the synchronization frame
and on a current time inside the ring intersection point node.
28. The optical network system according to claim 27, wherein the
master node is configured to determine an offset value to be set to
the specific node, based on a result of the measurement of the
propagation delay time between the master node and each of the
nodes other than the master node and on a result of the measurement
of the propagation delay time for one round on each of the upper
ring and the lower ring, also taking into account a direction of a
time slot, presence or absence of a jump over the master node,
presence or absence of a jump from the upper ring to the lower
ring, and presence or absence of a jump from the lower ring to the
upper ring.
29. An optical switch node connected to a master node via a
transmission path, comprising: a time slot synchronization unit
that is configured to, upon receipt of a control signal including a
time slot start time and a time stamp from the master node,
synchronize time slots at prescribed periods allocated to the
master node, and thereby give an instruction of transmitting or
receiving a data or performing route switching, based on a time
common to all of the optical switch nodes, the common time being
determined by setting a time shifted by a propagation delay time;
and an optical time slot switching unit that is configured to
transmit or receive a data or perform route switching in accordance
with the instruction from the time slot synchronization unit.
30. A master node which is connected to a plurality of optical
switch nodes via a transmission path, comprising: a time slot
synchronization unit that is configured to divide a wavelength path
having an arbitrary wavelength into a plurality of time slots each
having a prescribed time period and allocate the time slots to each
of the optical switch nodes; and an optical time slot switching
unit that is configured to deliver, to each of the optical switch
nodes, information for making each of the optical switch nodes
synchronize the time slots allocated thereto by the time slot
synchronization unit and thereby transmit or receive a data or
perform route switching, the information including a control signal
including a time slot start time and a time stamp, based on a time
common to all of the optical switch nodes, the common time being
determined by setting a time shifted by a propagation delay time.
Description
This application is a National Stage Application of
PCT/JP2013/066350, filed 13 Jun. 2013, which claims benefit of
Serial No. 2012-133776, filed 13 Jun. 2012 in Japan, Serial No.
2012-133775, filed 13 Jun. 2012 and Serial No. 2013-032134, filed
21 Feb. 2013 and which applications are incorporated herein by
reference. To the extent appropriate, a claim of priority is made
to each of the above disclosed applications.
TECHNICAL FIELD
The present invention relates to an optical network system, an
optical switch node, a master node, and a node.
BACKGROUND ART
An optical network system including an OADM (optical add/drop
multiplexer) has been known as an optical switch node. An ROADM
(Reconfigurable Optical Add/Drop Multiplexer), a type of the OADM,
is disclosed in a non-patent document of "HAGIMOTO Kazuo, and two
others, "Introduction to Optical Network Becoming More Familiar
(15)> (which will be referred to as Non-Patent Document 1
hereinafter). The OADM as its basic configuration is described
briefly below.
FIG. 146 is a block diagram illustrating an example of a
configuration of a conventional OADM. As illustrated in FIG. 146,
the OADM includes an optical SW (which may be used as an
abbreviation of a switch hereinafter) setting unit 501, an optical
SW unit 502, a demultiplexing unit 503, a multiplexing unit 504,
and transmit-receive units 505-1 to 505-N.
FIG. 147 is a diagram illustrating an example of a configuration of
a ring optical network system in which the OADMs illustrated in
FIG. 146 are connected in a ring shape via transmission lines.
As illustrated in FIG. 147, four OADMs 510A to 510D are installed
on land and are connected each other via a ring-shaped transmission
520. In a system illustrated in FIG. 147, a wavelength .lamda.1 is
allocated to an optical signal transmitted and received between the
OADM 510A and the OADM 510C. A wavelength .lamda.3 is allocated to
an optical signal transmitted and received between the OADM 510A
and the OADM 510D. A wavelength .lamda.2 is allocated to an optical
signal transmitted and received between the OADM 510B and the OADM
510C. And, a wavelength .lamda.4 is allocated to an optical signal
transmitted and received between the OADM 510B and the OADM 510D.
As described above, different wavelength paths having different
wavelengths are set for each point to point.
In a metro network which is established as the metropolitan area
optical network, as illustrated in "Key Points of Network for
Learner in One Week" (which will be referred to as Non-Patent
Document 2), wavelength division multiplexing (WDM) is used from a
viewpoint of band usage efficiency. As a network topology, a
ring-shaped one is used, for example. FIG. 148 is a diagram
illustrating a configuration of a conventional metro network. In
the metro network illustrated in FIG. 148, a plurality of
reconfigurable optical add/drop multiplexers (ROADMs) 530 are
installed as nodes into a ring-shaped optical fiber network 531.
Control of optical line switch type is provided using a wavelength
path, and an appropriate bandwidth is allocated, by statically
setting a wavelength path for each point to point in accordance
with an estimated maximum value of a point-to-point traffic volume.
In the illustrated example, a path having the wavelength .lamda.1
is set between a point A and a point D; and, .lamda.2, between a
point B and the point D. FIG. 149A and FIG. 149B are diagrams each
for explaining an operating principle of the conventional metro
network using the ROADM as described above. For example, different
paths having different wavelengths .lamda.1 to .lamda.3 are set
from the points A to C, respectively, to the point D as illustrated
in FIG. 149A. The point D thus receives temporally non-synchronous
data (Data1 to Data4) from the points A to C as illustrated in FIG.
149B.
In the conventional optical network as described above, because a
wavelength path is statically set for each point to point in
accordance with the estimated maximum traffic. Improvement of
bandwidth when a traffic volume is small becomes a problem to be
solved. For example, even if an actual point-to-point traffic
volume is smaller than an estimated value, which results in a free
device resource or bandwidth, it is not possible to use one free
bandwidth with a certain point-to-point wavelength path for a
communication between another point to point. Conversely, if a
given point-to-point traffic volume becomes larger than estimated,
it is not possible to transmit or receive part of data at the point
to point, using a wavelength path used in other point to point.
Further, the number of wavelengths as much as the number of points
to points need to be prepared, which causes a problem that the
number of points to points is limited depending on types of
wavelengths which the ROADM device can output.
An optical ring network (which may also be referred to as a "ring"
where appropriate) has been known which can improve traffic
accommodation efficiency by using a WDM technique and a TDM (Time
Division Multiplexing) technique. Multistage connection of a
plurality of such rings makes it possible to efficiently
accommodate traffic in a further wide area.
A non-patent document of "Demonstration of the Interconnection of
Two Optical Packet Rings with a Hybrid Optoelectronic Packet Router
(Alcatel, ECOC2010)" (which will be referred to as Non-Patent
Document 3) proposes a time slot (which may also be abbreviated to
a "TS" hereinafter) exchange method between WDM/TDM rings, in a
multi-ring network in which a plurality of the rings are connected
in multiple stages.
In the conventional method disclosed in Non-Patent Document 3,
adjustment of a fiber length between the rings allows time slots to
be exchanged at a ring intersection point (a node connecting
between rings), without collision between a time slot for
communication in an upper ring (which may also be referred to as a
first time slot) and a time slot for communication between rings
from a lower ring to the upper ring (which may also be referred to
as a second time slot).
RELATED ART DOCUMENTS
Non-Patent Documents
Non-Patent Document 1: HAGIMOTO Kazuo, and two others,
"Introduction to Optical Network Becoming More Familiar (15),
"ROADM" that can freely operate an optical core network, [online],
Jun. 15, 2006, Nikkei Business Publications, Inc., [searched on May
30, 2012], Internet
<URL:http://itpronikkeibp.co.jp/article/COLUMN/20060607/240199/>
Non-Patent Document 2: HAGIMOTO Kazuo, YAMABAYASHI Yoshiaki, and
TAKAHASHI Tetsuo, "[online], Jun. 15, 2006, "Key Points of Network
for Learner in One Week, Introduction to Optical Network Becoming
More Familiar (15), "ROADM" that can freely operate an optical core
network, [online], Nikkei Business Publications, Inc., Jun. 15,
2006, [searched on May 15, 2012], Internet
<URL:http://itpro.nikkeibp.co.jp/article/COLUMN/20060607/240199/>
Non-Patent Document 3: Demonstration of the Interconnection of Two
Optical Packet Rings with a Hybrid Optoelectronic Packet Router
(Alcatel, ECOC2010)
SUMMARY OF THE INVENTION
Problem to be Solved by the Invention
As illustrated in FIG. 147, in the conventional OADM, the number of
nodes which can be installed on a ring is limited by the number of
wavelengths, because different wavelengths need to be set to
different wavelength paths for each point-to-point. In the example
illustrated in FIG. 147, the number of the wavelengths is four,
namely, .lamda.1 to .lamda.4, while the number of nodes is also
four, namely, 510A to 510D. That is, in the conventional ring-type
optical network, the number of installable nodes is limited by the
number of wavelengths.
Further, in the optical network as the conventional metro network
using the WDM technique explained with reference to FIG. 148, FIG.
149A, and FIG. 149B, a wavelength path is statically set between
points. This has such problems that improvement of efficiency in
bandwidth usage cannot be expected and that it is not possible to
handle a situation in which a traffic volume between certain points
exceeds an estimated value.
In the conventional method disclosed in Non-Patent Document 3, in a
multi-ring network, adjustment of a fiber length between the rings
prevents collision between the first time slot and the second time
slot.
In an actual commercially-available network, however, the fiber
length varies depending on a change in outside air temperature.
This results in a change in a ring length and a deviation of
arrival timing of a time slot at a ring intersection point, which
causes a problem of collision between the first time slot and the
second time slot at the ring intersection point.
Also in a single ring network which is constituted by a single
ring, when a time slot operates periodically (at intervals of a
time t) at a master node as a source node on a ring (which may also
be referred to as an "optical master node" or a "source node"
hereinafter), if a processing timing of the time slot has a
propagation delay time of one round of a ring is not a multiple
integer of the time slot, a timing when a time slot transmitted
from other node arrives at the master node is deviated from the
time slot processing timing.
Thus, a problem occurs that the master node cannot process or
transfer a time slot which arrives from other node.
The present invention has been made in an attempt to solve the
above-described problems and provide an optical network system, an
optical switch node, a master node, and a node in which: the number
of nodes can be increased without depending on the number of
wavelengths; traffic accommodation efficiency of an entire system
can be improved by dynamic bandwidth allocation according to a
traffic volume, using the WDM technique; and a master node can
process and transfer a time slot which arrives from other node.
Means for Solving the Problem
An optical network system includes: a master node; and a plurality
of optical switch nodes. The master node is configured to divide a
wavelength path having an arbitrary wavelength into time slots each
having a prescribed time period, and allocate the time slots to
each of the optical switch nodes. Each of the optical switch nodes
is configured to synchronize the time slots based on information on
the allocation delivered from the master node, and thereby transmit
or receive a data or perform route switching.
An optical switch node is connected to a master node via a
transmission path. The optical switch node includes: a time slot
synchronization unit that is configured to synchronize time slots
at prescribed periods allocated to the master node, and thereby
give an instruction of transmitting or receiving a data or
performing route switching, based on information delivered from the
master node; and an optical time slot switching unit that is
configured to transmit or receive a data or perform route switching
in accordance with the instruction from the time slot
synchronization unit.
A master node is connected to a plurality of optical switch nodes
via a transmission path. The master node includes: a time slot
synchronization unit that is configured to divide a wavelength path
having an arbitrary wavelength into a plurality of time slots each
having a prescribed time period and allocate the time slots to each
of the optical switch nodes; and an optical time slot switching
unit that is configured to deliver, to each of the optical switch
nodes, information for making each of the optical switch nodes
synchronize the time slots allocated thereto by the time slot
synchronization unit and thereby transmit or receive a data or
perform route switching.
A node in an optical network system including a multi-ring network
in which a single ring network including a single ring or a
plurality of rings are connected in multiple stages, the node being
present on the ring. The node includes: a time slot control unit
that is configured to, if the node is a master node, set a time of
each of nodes other than the master node; a reference time slot
synchronization unit that is configured to, if the node is a node
other than the master node, tick a first time slot starting from
the time set by the master node; a delay measurement unit that is
configured to, if the node is the master node, calculate an offset
value of a specific node which is specified from among the nodes
other than the master node and set the calculated offset value to
the specific node, based on a propagation delay time between the
master node and each of the nodes other than the master node and on
a propagation delay time for one round on the ring; and a plural
time slot management unit that is configured to, if the node is the
specific node, tick a second time slot which is a time slot
starting from a timing shifted from a start timing of the first
time slot of its own node by the offset value set by the master
node.
Effects of the Invention
In the present invention, the number of nodes can be increased
without depending on the number of wavelengths.
In the present invention, a time TS allocation and a wavelength
allocation to each of the optical switch node can be changed in
accordance with an incoming traffic volume. This makes it possible
to achieve such advantageous effects that: a dynamic bandwidth
allocation can be realized in accordance with a point-to-point
traffic volume; traffic accommodation efficiency of the entire
system can be improved; and, with improvement of the traffic
accommodation efficiency, the number of wavelengths or receivers
used can be reduced.
Further, in the present invention, a master node makes each of
nodes other than the master node have time slots of up to two
types, based on a propagation delay time between the master node
and each of the nodes other than the master node and on a
propagation delay time for one round on a ring.
As described above, each of the nodes other than the master node is
provided with two types of time slots for data. Thus, in a case of
a multi-ring network, a node on a lower ring can have a time slot
for upper ring synchronized with a reference time slot of a ring
intersection point node. This makes it possible to achieve such an
advantageous effect that collision of time slots at the ring
intersection point node can be avoided.
In providing a time slot, a propagation delay time for one round of
a ring is taken into account. This makes it possible to achieve
such advantageous effects that, in a case of a single ring network,
even when the propagation delay time for one round of the ring is
not a multiple integer of the time slot, the master node can
perform a processing of a time slot arrived and can transfer a time
slot from other node.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a diagram illustrating a configuration example of an
optical network system according to an embodiment of the present
invention.
FIG. 2 is a functional block diagram for explaining a configuration
of an optical switch node of the optical network system illustrated
in FIG. 1.
FIG. 3 is a block diagram illustrating a configuration example of
the optical switch node according to a first embodiment.
FIG. 4 is a diagram schematically illustrating transmission routes
of a control signal and an optical signal in the optical switch
node illustrating in FIG. 3.
FIG. 5 is a block diagram illustrating a configuration example of a
master optical switch node according to the first embodiment.
FIG. 6 is a diagram schematically illustrating transmission routes
of a control signal and an optical signal in the master optical
switch node illustrated in FIG. 5.
FIG. 7 is a diagram illustrating a variation in a case where a
trigger is utilized with a TS start delivery function and a TS
synchronization function.
FIG. 8A is a schematic diagram when a trigger output interval of
FIG. 7 is a "TS length".
FIG. 8B is a schematic diagram when the trigger output interval of
FIG. 7 is a "TS period".
FIG. 8C is a schematic diagram when the trigger output interval of
FIG. 7 is a "TS period.times.N".
FIG. 9 is a diagram for explaining operations of No. 1001 of FIG.
7.
FIG. 10 is a diagram for explaining operations of No. 1002 of FIG.
7.
FIG. 11 is a diagram for explaining operations of No. 1004 of FIG.
7.
FIG. 12A is a time-series diagram for explaining how to set the TS
length and a TS period with respect to a ring length.
FIG. 12B is a system diagram for explaining how to set the TS
length and the TS period with respect to the ring length.
FIG. 13 is a diagram illustrating deviation of timing of a time
slot due to fluctuation.
FIG. 14 is a diagram illustrating a data and guard times in a time
slot.
FIG. 15 is a block diagram illustrating an example of a
configuration in a case where a physical topology is a
unidirectional ring.
FIG. 16 is a block diagram illustrating an example of a
configuration in a case where the physical topology is a
bidirectional ring.
FIG. 17A is a diagram illustrating a variation example of a
configuration of trigger transmission.
FIG. 17B is a diagram illustrating another variation example of the
configuration of trigger transmission.
FIG. 18A is a diagram illustrating a still another variation
example of the configuration of trigger transmission.
FIG. 18B is a diagram illustrating a yet another variation example
of the configuration of trigger transmission.
FIG. 19A is a diagram illustrating a configuration example in a
case where connection between a TS transmit-receive unit and an
optical TS-SW unit is configured as one input and one output.
FIG. 19B is a diagram illustrating a configuration example in a
case where connection between the TS transmit-receive unit and the
optical TS-SW unit is configured as one input and an output for
each queue.
FIG. 19C is a diagram illustrating a configuration example in a
case where connection between a TS transmit-receive unit and the
optical TS-SW unit is configured as two inputs and an output for
each queue.
FIG. 20A is a diagram for explaining a variation of how to supply a
clock.
FIG. 20B is a diagram for explaining another variation of how to
supply a clock.
FIG. 21 is a block diagram illustrating a configuration example of
an optical switch node according to a second embodiment.
FIG. 22 is a diagram schematically illustrating transmission routes
of a control signal and an optical signal in the optical switch
node illustrated in FIG. 21.
FIG. 23 is a block diagram illustrating a configuration example of
a master optical switch node according to the second
embodiment.
FIG. 24 is a diagram schematically illustrating transmission routes
of a control signal and an optical signal in the master optical
switch node illustrated in FIG. 23.
FIG. 25 is a schematic diagram when a trigger output interval is a
"TS length" in an optical network system according to the second
embodiment.
FIG. 26 is a block diagram illustrating a configuration example of
an optical switch node according to a third embodiment.
FIG. 27 is a diagram schematically illustrating transmission routes
of a control signal and an optical signal in the optical switch
node illustrated in FIG. 26.
FIG. 28 is a block diagram illustrating a configuration example of
a master optical switch node according to the third embodiment.
FIG. 29 is a diagram schematically illustrating transmission routes
a control signal and an optical signal in the master optical switch
node illustrated in FIG. 28.
FIG. 30 is a block diagram illustrating a configuration example of
an optical switch node according to a fourth embodiment.
FIG. 31 is a diagram schematically illustrating transmission routes
of a control signal and an optical signal in the optical switch
node illustrated in FIG. 30.
FIG. 32 is a block diagram illustrating a configuration example of
a master optical switch node according to the fourth
embodiment.
FIG. 33 is a diagram schematically illustrating transmission routes
of a control signal and an optical signal in the master optical
switch node illustrated in FIG. 32.
FIG. 34 is a diagram illustrating a variation in a case where a
time is utilized with a TS start delivery function and a TS
synchronization function, and a time counter is set at a time with
a delay difference added thereto.
FIG. 35 is a diagram for explaining operations of No. 2002 of FIG.
34.
FIG. 36A is a system diagram for explaining how to set a time to
which a transmission path delay time is added.
FIG. 36B is a time-series diagram for explaining how to set the
time to which the transmission path delay time is added.
FIG. 37A is a diagram for explaining a variation of how to set a
time with delay.
FIG. 37B is a diagram for explaining another variation of how to
set the time with delay.
FIG. 38 is a block diagram illustrating a configuration example in
which a physical topology is a unidirectional ring.
FIG. 39A is a block diagram illustrating a configuration example in
which the physical topology is a bidirectional ring.
FIG. 39B is a block diagram illustrating another configuration
example in which the physical topology is a bidirectional ring.
FIG. 40 is a diagram for explaining a DROP switching time of a
master node.
FIG. 41 is a diagram illustrating an example of how to set TS
information on the master node.
FIG. 42 is a diagram for explaining how to calculate and set a ring
one-round time.
FIG. 43 is a diagram illustrating a variation in a case where a
time counter is set at a common time.
FIG. 44 is a block diagram illustrating a configuration example of
an optical switch node according to a fifth embodiment.
FIG. 45 is a diagram schematically illustrating transmission routes
of a control signal and an optical signal in the optical switch
node illustrated in FIG. 44.
FIG. 46 is a block diagram illustrating a configuration example of
a master optical switch node according to a fifth embodiment.
FIG. 47 is a diagram schematically illustrating transmission routes
of a control signal and an optical signal in the master optical
switch node illustrated in FIG. 46.
FIG. 48 is a diagram illustrating a configuration example of an
optical network system according to the fifth embodiment.
FIG. 49A is a system diagram for explaining a TS start time in a
case where a common time is set.
FIG. 49B is a time-series diagram for explaining the TS start time
in a case where a common time is set.
FIG. 50 is a diagram for explaining how to measure a delay
time.
FIG. 51 is a diagram classifying optical TS-SW units applicable to
the first to fifth embodiments.
FIG. 52 is a diagram for explaining a configuration of an optical
TS-SW unit according to Example 1.
FIG. 53 is a diagram for explaining a configuration of an optical
TS-SW unit according to Example 2.
FIG. 54 is a diagram for explaining a configuration of an optical
TS-SW unit according to Example 3.
FIG. 55 is a diagram for explaining a configuration of an optical
TS-SW unit according to Example 4.
FIG. 56 is a diagram for explaining a configuration of an optical
TS-SW unit according to Example 5.
FIG. 57A is a diagram for explaining a configuration of an optical
TS-SW unit according to Example 6.
FIG. 57B is a diagram illustrating TWC wavelength requirements of
the optical TS-SW unit according to Example 6.
FIG. 58A is a diagram for explaining a configuration of an optical
TS-SW unit according to Example 7.
FIG. 58B is a diagram illustrating TWC wavelength requirements of
the optical TS-SW unit according to Example 7.
FIG. 59A is a diagram for explaining a configuration of an optical
TS-SW unit according to Example 8.
FIG. 59B is a diagram illustrating TWC wavelength requirements of
the optical TS-SW unit according to Example 8.
FIG. 60 is a block diagram illustrating a configuration example of
an optical TS-SW unit including TWCs and FWCs.
FIG. 61 is a block diagram illustrating a configuration example of
the TWC illustrated in FIG. 60.
FIG. 62 is a block diagram illustrating a configuration example of
the FWC illustrated in FIG. 60.
FIG. 63 is a block diagram illustrating a basic structure of a
spatial switch of broadcast and select type.
FIG. 64 is a diagram illustrating another example of the spatial
switch of broadcast and select type.
FIG. 65A is a system diagram for explaining an outline of
operations of an optical network of the present invention.
FIG. 65B is a time-series diagram for explaining the outline of
operations of the optical network of the present invention.
FIG. 66A is a diagram illustrating a network configuration of an
optical network according to an embodiment of the present
invention.
FIG. 66B is a timing diagram illustrating data transmission
timing.
FIG. 67A is a block diagram illustrating a configuration of a
master node of trigger type configuration according to the
embodiment of the present invention.
FIG. 67B is a block diagram illustrating a configuration of an
optical switch node of trigger type configuration according to the
embodiment of the present invention.
FIG. 68A is a block diagram illustrating a configuration of a
master node of time synchronization type configuration according to
the embodiment of the present invention.
FIG. 68B is a block diagram illustrating a configuration of an
optical switch node time synchronization type configuration
according to the embodiment of the present invention.
FIG. 69 a time sequence diagram illustrating a processing of
notifying traffic information.
FIG. 70 is a diagram for explaining how to predict a buffer
overflow.
FIG. 71 is a diagram for explaining an example of information
notified from the TS transmit-receive unit.
FIG. 72 is a diagram illustrating various assumed examples when TS
start delivery and TS synchronization is performed using a
trigger.
FIG. 73 is a diagram for explaining a relation between a time slot
and a trigger in the trigger type configuration.
FIG. 74 is a diagram for explaining an example of operations of the
TS start delivery and the TS synchronization in the trigger type
configuration.
FIG. 75 is a diagram for explaining another example of the
operations of the TS start delivery and the TS synchronization in
the trigger type configuration.
FIG. 76 is a diagram for explaining a still another example of the
operations of the TS start delivery and the TS synchronization in
the trigger type configuration.
FIG. 77A is a diagram illustrating a ring-shaped network
configuration.
FIG. 77B is a diagram illustrating a relation among the ring
length, the TS (time slot) length, and the TS period.
FIG. 78 is a diagram for explaining deviation of timing of a time
slot due to clock fluctuation.
FIG. 79 is a diagram for explaining a relation between a data and a
guard time in a time slot.
FIG. 80A is a diagram for explaining a ring topology of an optical
switch node on a unidirectional ring in the trigger type
configuration.
FIG. 80B is a diagram for explaining a ring topology of an optical
switch node on a bidirectional ring in the trigger type
configuration.
FIG. 81 is a diagram for explaining time setting using a time with
delay difference.
FIG. 82 is a diagram for explaining an example of how to deliver a
control signal for setting in the time synchronization type
configuration using the time with delay difference.
FIG. 83A is a diagram for explaining counterclockwise setting in
the time synchronization type configuration using the time with
delay difference.
FIG. 83B is a diagram for explaining clockwise setting in the time
synchronization type configuration using the time with delay
difference.
FIG. 84A is a system diagram for explaining an example of how to
set a time in the time synchronization type configuration using the
time with delay difference.
FIG. 84B is a time-series diagram for explaining the example of how
to set a time in the time synchronization type configuration using
the time with delay difference.
FIG. 85A is a system diagram for explaining an example of how to
measure a delay in the time synchronization type configuration
using the time with delay difference.
FIG. 85B is a time-series diagram for explaining the example of how
to measure a delay in the time synchronization type configuration
using the time with delay difference.
FIG. 86A is a diagram for explaining a ring topology of an optical
switch node on a unidirectional ring in the time synchronization
type configuration using the time with delay difference.
FIG. 86B is a diagram for explaining a ring topology of an optical
switch node on a bidirectional ring in the time synchronization
type configuration using the time with delay difference.
FIG. 87A is a system diagram for explaining a DROP switching time
at a master node in the time synchronization type configuration
using the time with delay difference.
FIG. 87B is a diagram for explaining an example of a setting of
time slot information of a master node in the time synchronization
type configuration using the time with delay difference.
FIG. 88 is a diagram for explaining an example of operations of how
a local time and a TS start time is delivered in the time
synchronization type using the time with delay difference.
FIG. 89 is a diagram for explaining time synchronization using a
common time.
FIG. 90A is a system diagram for explaining how to deliver a time
and how to measure a delay in the time synchronization type
configuration using the common time.
FIG. 90B is a time-series diagram for explaining how to deliver the
time and how to measure a delay in the time synchronization type
configuration using the common time.
FIG. 91A is a system diagram for explaining a TS start time in the
time synchronization type configuration using the common time.
FIG. 91B is a time-series diagram for explaining the TS start time
in the time synchronization type configuration using the common
time.
FIG. 92 is a time sequence diagram illustrating a processing of
recognizing a topology in a case of a single control ring.
FIG. 93A is a block diagram illustrating a variation of a
configuration for transmitting a trigger (or a control signal).
FIG. 93B is a block diagram illustrating another variation of the
configuration for transmitting a trigger (or a control signal).
FIG. 93C is a block diagram illustrating a still another variation
of the configuration for transmitting a trigger (or a control
signal).
FIG. 93D is a block diagram illustrating a yet another variation of
the configuration for transmitting a trigger (or a control
signal).
FIG. 94A is a block diagram illustrating a configuration example of
connection between the TS transmit-receive unit and the optical
TS-SW unit.
FIG. 94B is a block diagram illustrating another configuration
example of connection between the TS transmit-receive unit and the
optical TS-SW unit.
FIG. 94C is a block diagram illustrating a still another
configuration example of connection between the TS transmit-receive
unit and the optical TS-SW unit.
FIG. 95A is a diagram illustrating an outline of a configuration of
an optical TS-SW unit (a wavelength switch).
FIG. 95B is a diagram illustrating an outline of another
configuration of the optical TS-SW unit (the wavelength
switch).
FIG. 96 is a block diagram illustrating a basic configuration of
the optical TS-SW unit.
FIG. 97A is a block diagram illustrating a structure of a variable
wavelength converter (TWC).
FIG. 97B is a block diagram illustrating a structure of a fixed
wavelength converter (FWC).
FIG. 98 is a diagram illustrating various configurations of the
optical TS-SW unit of wavelength switch type.
FIG. 99 is a block diagram illustrating a configuration example of
the optical TS-SW unit using a k-fold ring.
FIG. 100 is a block diagram illustrating a configuration example of
the optical TS-SW unit in a case of a double ring, 1 ADD 1 DROP,
and inter-fiber exchangeability.
FIG. 101 is a block diagram illustrating a configuration example of
the optical TS-SW unit in a case of a double ring, 1 ADD 1 DROP,
and inter-fiber exchangeability, using a wavelength for
control.
FIG. 102 is a block diagram illustrating another configuration
example of the optical TS-SW unit in a case of a double ring, 1 ADD
1 DROP, and inter-fiber exchangeability.
FIG. 103 is a block diagram illustrating a configuration example of
the optical TS-SW unit in which inter-fiber wavelength exchange and
in-fiber wavelength exchange is possible, without using the
FWC.
FIG. 104 is a block diagram illustrating a configuration example of
the optical TS-SW unit in a case of a double ring, 1 ADD 1 DROP,
and 1 AWG per 1 fiber, using a wavelength for control.
FIG. 105A is a block diagram illustrating a configuration example
of the optical TS-SW unit in a case of a double ring and ADD/DROP 1
channel, using the FWC.
FIG. 105B is a diagram illustrating TWC wavelength requirements of
the optical TS-SW unit.
FIG. 106A is a block diagram illustrating a configuration example
of the optical TS-SW unit in a case of a double ring and ADD/DROP 1
channel, using the FWC.
FIG. 106B is diagram illustrating TWC wavelength requirements of
the optical TS-SW unit.
FIG. 107A is a block diagram illustrating a configuration example
of the optical TS-SW unit in a case of a double ring and ADD/DROP 1
channel, and inter-fiber and in-fiber wavelength exchangeability,
using the FWC.
FIG. 107B is a diagram illustrating TWC wavelength requirements of
the optical TS-SW unit.
FIG. 108 is a diagram illustrating a basic configuration of the
optical TS-SW unit of broadcast and select type.
FIG. 109 is a diagram illustrating an example of another
configuration of the optical TS-SW unit of broadcast and select
type.
FIG. 110 is a diagram for explaining a definition of time slot
synchronization.
FIG. 111 is a diagram for explaining a basic idea of the present
invention.
FIG. 112 is a diagram for explaining how to synchronize a time slot
and a ring intersection point node on a lower ring.
FIG. 113 is a diagram for explaining a functional block of each
node.
FIG. 114 is a diagram for explaining definitions of an M-C, a Sub
M-C, and an S-C.
FIG. 115A is a system diagram for explaining how to set a time slot
start timing from a source node.
FIG. 115B is a time-series diagram for explaining how to set the
time slot start timing from the source node.
FIG. 116 is a system diagram for explaining how to set a time at
each of nodes.
FIG. 117A is a system diagram for explaining an advantageous effect
of the setting of a time slot start timing.
FIG. 117B is a time-series diagram for explaining the advantageous
effect of the setting of the time slot start timing.
FIG. 118 is a diagram for explaining how to measure a propagation
delay time between adjacent nodes.
FIG. 119A is a diagram for explaining how to measure a propagation
delay time.
FIG. 119B is another diagram for explaining how to measure the
propagation delay time.
FIG. 120 is a diagram for explaining how to measure a propagation
delay time for one round on a ring.
FIG. 121 is a diagram for explaining a timing separation between an
ADD onto an upper ring and a DROP onto a lower ring, taking a
propagation delay into account.
FIG. 122A is a system diagram for explaining a time slot from a
lower ring to an upper ring.
FIG. 122B is a time-series diagram for explaining the time slot
from the lower ring to the upper ring.
FIG. 123A is a system diagram for explaining various types of time
slots required when a bidirectional communication is performed on a
multi-ring.
FIG. 123B is a diagram for explaining the various types of the time
slots required when the bidirectional communication is performed on
the multi-ring.
FIG. 124A is a diagram for explaining a time slot used in a single
ring network (in a forward direction).
FIG. 124B is a diagram for explaining another time slot used in the
single ring network (in the forward direction).
FIG. 124C is a still another diagram for explaining a time slot
used in a single ring network (in the forward direction).
FIG. 125A is a diagram for explaining a time slot used in a single
ring network (in a backward direction).
FIG. 125B is a diagram for explaining another time slot used in the
single ring network (in the backward direction).
FIG. 125C is a diagram for explaining a still another time slot
used in the single ring network (in the backward direction).
FIG. 126A is a diagram for explaining another example of a time
slot used in a multi-ring network (in a forward direction).
FIG. 126B is a diagram for explaining a still another example of
the time slot used in the multi-ring network (in the forward
direction).
FIG. 126C is a diagram for explaining a yet another example of the
time slot used in the multi-ring network (in the forward
direction).
FIG. 126D is a diagram for explaining a further example of the time
slot used in the multi-ring network (in the forward direction).
FIG. 127A is a diagram for explaining an example of a time slot
used in a multi-ring network (in the backward direction).
FIG. 127B is a diagram for explaining another example of the time
slot used in the multi-ring network (in the backward
direction).
FIG. 127C is a diagram for explaining a still another example of
the time slot used in the multi-ring network (in the backward
direction).
FIG. 127D is a diagram for explaining a yet another example of the
time slot used in the multi-ring network (in the backward
direction).
FIG. 128 is a diagram for explaining an operating sequence when an
operation of delivering a time counter value at an M-C is
started.
FIG. 129 is a diagram for explaining an operating sequence when
information on delivery of the time counter value at the M-C is
set.
FIG. 130 is a diagram for explaining an operating sequence when an
initial time counter value at the M-C is delivered to an upper
ring.
FIG. 131 is a diagram for explaining an operating sequence when the
initial time counter value is received at a SubM-C on the upper
ring.
FIG. 132 is a diagram for explaining an operating sequence when
information on delivery of the time counter value to a lower ring
at the M-C is set.
FIG. 133 is a diagram for explaining an operating sequence when an
initial time counter value at the M-C is delivered to the lower
ring.
FIG. 134 is a diagram for explaining an operating sequence when a
time is responded at the S-C on the lower ring.
FIG. 135 is a diagram for explaining an operating sequence when a
time response of the S-C is transferred at the Sub M-C.
FIG. 136A is a system diagram for explaining an operating sequence
when the time response of the S-C is transferred at the Sub
M-C.
FIG. 136B is a diagram for explaining the operating sequence when
the time response of the S-C is transferred at the Sub M-C.
FIG. 137 is a diagram for explaining a timing of generating a time
slot suited for a backward direction/M-C jump.
FIG. 138 is a diagram for explaining how to generate a backward
direction time slot.
FIG. 139 is a diagram for explaining how to generate a forward
direction jump time slot.
FIG. 140 is a diagram for explaining how to generate a backward
direction jump time slot.
FIG. 141 is a diagram for explaining a first implementation example
of a node on a lower ring.
FIG. 142 is a diagram for explaining a second implementation
example of a node on a lower ring.
FIG. 143 is a diagram for explaining a multi-ring network to which
the present invention is directed.
FIG. 144 is a diagram for explaining a single ring network to which
the present invention is directed.
FIG. 145 is a diagram for explaining problems in conventional
technologies and specific means for solving the problems by the
present invention.
FIG. 146 is a block diagram illustrating an example of a
configuration of a conventional OADM.
FIG. 147 is a diagram illustrating an example of a configuration of
a ring optical network system in which the OADMs illustrated in
FIG. 146 are connected in a ring shape via a transmission path.
FIG. 148 is a diagram illustrating an example of a conventional
metro network.
FIG. 149A is a diagram illustrating an example of a configuration
of an optical network by wavelength division multiplexing using
ROADMs.
FIG. 149B is a diagram for explaining an operating principle of the
optical network by wavelength division multiplexing using the
ROADMs.
EMBODIMENTS FOR CARRYING OUT THE INVENTION
A configuration of an optical network system according to an
embodiment of the present invention is described below.
FIG. 1 is an example of a configuration of an optical network
system according to an embodiment of the present invention.
As illustrated in FIG. 1, the optical network system has a
configuration in which optical switch nodes (each of which may be
simply referred to as a "node" hereinafter) 101A to 101D are
connected via a transmission path (a physical path). It is assumed
herein that the optical switch node 101A is a master node (an
optical master node). Note that FIG. 1 illustrates a case in which
the number of the optical switch nodes 101A to 101D is four. The
number of the optical switch nodes is not, however, limited to
four, and may be any number more than one. The transmission path
may also be referred to as a ring.
The optical switch node 101A divides a wavelength path having a
given wavelength .lamda.x into time slots each having a
predetermined time period and allocates the time slots to the
optical switch nodes 101B to 101D. The optical switch nodes 101B to
101D each synchronize the time slot (which may also be referred to
as a "TS" hereinafter) based on information delivered from the
optical switch node 101A as the master node and transmits or
receives data appropriately.
FIG. 2 is a functional block diagram for explaining a configuration
of the optical switch nodes in the optical network system
illustrated in FIG. 1.
Each of the optical switch nodes 101A to 101D includes: a time slot
synchronization unit 151; an optical TS-SW unit (an optical time
slot switching unit) 152 as a wavelength switch; and a TS
transmit-receive unit 153 that transmits or receives data between
the routers or the like 103A to 103D illustrated in FIG. 1 and the
optical TS-SW unit 152. Note that the TS-SW used herein is an
abbreviation for a time slot switch and may also be used
hereinafter.
In the optical switch node 101A (which may also be referred to as
the master node 101A) which serves as the master node, the time
slot synchronization unit 151 divides a wavelength path having an
arbitrary wavelength into time slots each having a predetermined
time period and allocates the time slots to the optical switch
nodes 101B to 101D. The optical TS-SW unit 152 of the master node
101A synchronizes the time slots allocated by the synchronization
unit 151 to the optical switch nodes 101B to 101D and delivers
information for executing data transmission and receipt to the
optical switch nodes 101B to 101D.
In each of the optical switch nodes 101B to 101D, the time slot
synchronization unit 151 synchronizes the time slots each having a
predetermined time and allocated by the master node 101A, based on
the information delivered from the optical switch node 101A, and
instructs the optical TS-SW unit 152 to transmit or receive data.
The optical TS-SW unit 152 of each of the optical switch nodes 101B
to 101D transmits or receives the data following the instruction
from the time slot synchronization unit 151.
Note that FIG. 1 illustrates a state in which the optical switch
nodes 101A to 101D hold time slot information showing contents of
instructions on data processing. The time slot information herein
may be previously stored in each of the nodes or may be delivered
from the master node 101A to the optical switch nodes 101B to
101D.
In the above-described optical network system, a wavelength path is
divided into time slots each having a predetermined time period;
the time slots are allocated to respective nodes; and, based on the
allocated time slots, the nodes each transmit or receive data or
perform route switching. The TS synchronization unit 151 controls
the TS transmit-receive unit 153 and the optical TS-SW unit 152
illustrated in FIG. 2 such that the nodes synchronize the data
transmission and the route switching so as to prevent data from
colliding in the same wavelength path and to enable data
transmission or ADD (insertion)/DROP (branch) by the allocated time
slot of its own. One of methods of establishing the synchronization
is a method based on a trigger from the master node 101A and
another is a method based on a time.
The present invention makes it possible to realize an optical TDM
ring system which does not depend on the number of wavelength
paths. Also, reduction in the numbers of wavelengths and receivers
required for the nodes 101A to 101D becomes possible.
Next is described the optical network system according to this
embodiment more specifically.
First Embodiment
In the optical network system according to the first embodiment,
when the master node transmits a trigger to each of nodes, time
slots (TSs) of the nodes are synchronized. The master node then
sets a TS length or a TS period at one over the integers. This
makes it possible to match a timing at which the trigger is
terminated at the master node after one round of a ring, and a
timing at which another trigger is outputted, thus allowing
periodic data transmission and receipt to be realized in the ring
network.
Next is described a configuration of the optical switch node
according to this embodiment.
FIG. 3 is a block diagram illustrating an example of a
configuration of an optical switch node 1 according to this
embodiment. FIG. 4 is a diagram schematically illustrating
transmission routes of a control signal and an optical signal in
the optical switch node 1 illustrated in FIG. 3. Broken arrows show
directions in which the control signal is transmitted, and solid
arrows show directions in which the optical signal is transmitted.
The same is applied to other block diagrams to be described
hereinafter.
As illustrated in FIG. 3, the optical switch node 1 includes: a TS
information management unit 10 that sets TS information; a TS
synchronization unit (time slot synchronization unit) 20; an
optical TS-SW unit 30; and a TS transmit-receive unit 40. The TS
synchronization unit 20 includes: a trigger detection unit 21; an
optical SW control unit 22; and a transmission control unit 23. The
optical TS-SW unit 30 is connected to a demultiplexing unit 31 on
an input side of an optical signal and a multiplexing unit 32 on an
outputs side of the optical signal.
Next description is made with reference to FIG. 4. The TS
information management unit 10 includes a storage unit (not shown)
for storing therein TS information. In this embodiment, though
described later, the TS information contains a TS length or a TS
period which is set at one over the integers of a length of a ring.
The TS information also contains details of an instruction on a
data processing such as information on a destination node of data
and an operation to data. The operation used herein is DROP, ADD,
and the like.
The trigger detection unit 21 detects a trigger for synchronizing a
start timing of a time slot set to each node and notifies the
optical SW control unit 22 and the transmission control unit 23 of
the detected result.
The optical SW control unit 22: counts an elapsed time from receipt
of the trigger detection notification; references the TS
information management unit 10; and instructs the optical TS-SW
unit 30 to switch a route with a time slot allocated thereto.
The optical TS-SW unit 30 switches the route in accordance with the
instruction from the optical SW control unit 22.
The transmission control unit 23: counts an elapsed time from the
receipt of the trigger detection notification; references the TS
information management unit 10; and instructs the TS
transmit-receive unit 40 to transmit the data with a time slot
allocated to itself.
The TS transmit-receive unit 40: stores the data inputted from
outside in a buffer (not shown), transmits data read out from the
buffer in accordance with an instruction from the transmission
control unit 23, to the optical TS-SW unit 30; and transmits a data
received from the optical TS-SW unit 30 to the outside. The outside
used herein refers to, for example, a communication device such as
the routers or the like 103A to 103D illustrated in FIG. 1.
The demultiplexing unit 31 wavelength-demultiplexes an optical
signal inputted from the outside via the transmission path and
outputs the optical signal to the optical TS-SW unit 30. The
multiplexing unit 32 wavelength-multiplexes the optical signal
inputted from the optical TS-SW unit 30 and outputs the optical
signal to the outside via the transmission path. Note that the
demultiplexing unit 31 and the multiplexing unit 32 are not
necessarily provided. Instead of providing the demultiplexing unit
31 and the multiplexing unit 32, the number of fibers of the
transmission path may be increased.
Next is described a configuration of a master optical switch node
(which may also be referred to as a master node) in this
embodiment.
FIG. 5 is a block diagram illustrating a configuration example of a
master node 2 in this embodiment. FIG. 6 is a diagram schematically
illustrating the master node 2 in this embodiment. FIG. 6 is a
diagram schematically illustrating transmission routes of a control
signal and an optical signal in the master node 2 illustrated in
FIG. 5.
As illustrated in FIG. 5, the master node 2 has a configuration
similar to that explained with reference to FIG. 3, except that the
master node 2 further includes a trigger generation unit 50 that
generates a trigger for synchronizing time slots and transmits the
trigger to the node, The trigger generation unit 50 sets a
transmission period at any one of a "TS length", a "TS period", and
a "TS period.times.N".
Next is described a variation in a case where a trigger is used
with a TS start delivery function 50a of the trigger generation
unit 50 and a TS synchronization function 20a of the TS
synchronization unit 20.
FIG. 7 is a diagram illustrating a variation in a case where a
trigger is utilized with the TS start delivery function 50a and the
TS synchronization function 20a. As illustrated in FIG. 7, a
trigger output interval can be selected from the "TS length", the
"TS period", and the "TS period.times.N".
FIGS. 8A to 8C are diagrams schematically illustrating TS output
units in cases of the "TS length" (which may also be referred to as
.asterisk-pseud.1 hereinafter), the "TS period"
(.asterisk-pseud.2), and the "TS period.times.N"
(.asterisk-pseud.3) illustrated in FIG. 7, respectively. FIG. 8A is
a schematic diagram when the trigger output interval is the "TS
length". FIG. 8B is a schematic diagram when the trigger output
interval is the "TS period". FIG. 8C is a schematic diagram when
the trigger output interval is the "TS period.times.N".
Next are described operations of the optical network system in this
embodiment. Firstly, operations when the trigger output interval is
the "TS length" are described.
FIG. 9 is a diagram for explaining operations of No. 1001
illustrated in FIG. 7. Referring to FIG. 9, operations are
described when a data is transmitted using an optical signal, from
node A to node B, from node A to node C, and from node B to node C,
in which all of the nodes are other than the master node 2.
TS information is previously set to each of nodes A to C. The TS
information having been set to node A and node B is exemplified in
[1] and [2] of FIG. 9, respectively. TS numbers "0" to "2"
allocated as an ADD to any one of wavelengths correspond one-to-one
with nodes A to C. The TS length is set at one over the integers of
a length of a ring.
As illustrated in [3], the master node 2 transmits the trigger at
intervals of the TS length (20 .mu.sec) to node A. The trigger
makes one round of the ring and is then terminated. The unit of the
TS length is assumed to be .mu.sec hereinafter.
Upon receipt of the trigger, node A performs the first operation of
the TS information after an offset time (5 .mu.sec) as illustrated
in [4]. Herein, the unit of the offset time is .mu.sec. In some
cases depending on a time counting operation of a system, 5 .mu.sec
is represented as 5 counts, for example. Thus, the unit of the
offset time may also be referred to as a count.
That is, node A performs an ADD of a data of node B to TS0 as
illustrated in line 1 of [1]. At this time, an optical SW
connection port is connected from port No. 3 to port No. 2. Upon
receipt of a subsequent trigger, node A similarly performs the
second operation of the TS information. Upon receipt of another
subsequent trigger, node A similarly performs the third operation
of the TS information. That is, node A performs an ADD of a data of
node C as a destination to TS2, as illustrated in line 3 of [1]. At
this time, the optical SW connection port is connected from port
No. 3 to port No. 2.
Upon receipt of the trigger, node B performs the first operation of
the TS information after an offset time (5 .mu.sec), as illustrated
in [5]. That is, node B performs a DROP of the data at TS0, as
illustrated in [2]. At this time, an optical SW connection port is
connected from port No. 1 to port No. 3. Upon receipt of a
subsequent trigger, node B similarly performs the second operation
of the TS information. That is, node B performs an ADD of the data
of node C as the destination to TS1, as illustrated in [2]. At this
time, an optical SW connection port is connected from port No. 3 to
port No. 2.
Next are described operations when the trigger output interval is
the "TS period".
FIG. 10 is a diagram for explaining operations in a case of No.
1002 illustrated in FIG. 7. Referring to FIG. 10, the operations
are described when a data is transmitted from node A to node B,
from node A to node C, and from node B to node C, using an optical
signal.
TS information is previously set to each of nodes A to C. The TS
information having been set to node A and node B is exemplified in
[1] and [2] of FIG. 10, respectively. TS numbers "0" to "2"
allocated as an ADD to any one of wavelengths correspond one-to-one
to nodes A to C. The TS length is set such that the TS period (TS
length.times.m) be one over the integers of a length of a ring.
As illustrated in [3], the master node 2 transmits a trigger to
node A at intervals of the TS period. After making one round of a
ring, the trigger is terminated.
Upon receipt of the trigger, after an offset time elapses (for
example, 5 counts herein) as illustrated in [4], node A performs
the first to m-th operations of the TS information. That is, as
illustrated in [1], after the offset time, node A performs: an ADD
of a data of node B as a destination, to TS0, and; after 45 counts
(Offset time+TS number.times.TS length=5+2.times.20), also performs
an ADD of a data of node C as a destination to TS2. At this time,
an optical SW connection port is connected from port No. 3 to port
No. 2.
Upon receipt of the trigger, node B sequentially performs the first
to m-th operations of the TS information after the offset time (5
counts) as illustrated in [5]. That is, also as illustrated in [2],
after an offset time, node B performs a DROP of TS0, and, after 25
counts (Offset time+TS number.times.TS length=5+1.times.20),
performs an ADD of a data of node C as a destination to TS1. At the
DROP, the optical SW connection port is connected from port No. 1
to No. 3, and, at the ADD, from port No. 3 to port No. 2.
Next are described operations when the trigger output interval is
the "TS period.times.N".
FIG. 11 is a diagram for explaining operations in a case of No.
1004 illustrated in FIG. 7. Referring to FIG. 11, operations are
described when a data is transmitted from node A to node B, from
node A to node C, and from node B to node C, using an optical
signal.
TS information is previously set to each of nodes A to C. The TS
information having been set to node A and node B is exemplified in
[1] and [2] of FIG. 11, respectively. TS numbers "0" to "2"
allocated as an ADD to any one of wavelengths correspond one-to-one
to nodes A to C. The TS length is set such that the TS period (TS
length.times.m) is one over the integers of the length of the
ring.
As illustrated in [3], the master node 2 transmits the trigger to
node A at intervals of the TS period.times.N. After making one
round of a ring, the trigger is terminated.
Upon receipt of the trigger, node A performs the first to m-th
operations of the TS information after an offset time (5 counts
herein) as illustrated in [4]. Upon receipt of a subsequent
trigger, similarly to the first trigger, node A repeats the first
to m-th operations of the TS information. That is, as illustrated
in line 1 of [1], after the offset time, node A performs an ADD of
a data of node B as a destination to TS0, and then, as illustrated
in line 3 of [1], performs an ADD of a data of node C as a
destination to TS2. At this time, the optical SW connection port is
connected from port No. 3 to port No. 2.
Upon receipt of the trigger, node B sequentially performs the first
to m-th operations of the TS information after the offset time (5
counts) as illustrated in [5]. After performing the m-th operation,
node B repeats the first to m-th operations until node B receives a
subsequent trigger. Upon receipt of the subsequent trigger,
similarly to the first trigger, node B repeats the first to m-th
operations of the TS information. That is, as illustrated in [2],
node B performs a DROP of a data of TS0, and then, performs an ADD
of a data of node C as a destination to TS1. At the DROP, the
optical SW connection port is connected from port No. 1 to No. 3,
and, at the ADD, from port No. 3 to port No. 2.
Next is described how to set a TS length and a TS period with
respect to a ring length.
FIG. 12A and FIG. 12B are diagrams each for explaining how to set a
TS length and a TS period with respect to a ring length.
In an optical ring system, nodes A to C transmit or receive data
each other in a transmission path shown with a broken line in a
ring-like shape. Thus, in order to receive a data across the master
node 2, such as "from node C to node A" (see FIG. 12A), the TS
length or the TS period is set to be one over the integers of a
ring length L. More specifically, when the trigger output interval
is the TS length, the TS length is set at one over the integers of
the ring length L. When the trigger output interval is the TS
period or the TS period.times.N, the TS period is set at one over
the integers of the ring length L. This makes it possible for node
A to receive a data transmitted from node C, using a trigger newly
transmitted from the master node 2.
Next is described how to deal with deviation of timing of a time
slot.
FIG. 13 is a diagram illustrating deviation of timing of a time
slot due to fluctuation. FIG. 14 is a diagram illustrating a data
and guard times in a time slot.
Transmission and reception timing of time slots of nodes A to C are
deviated in some cases as illustrated with clocks CK1 and CK2 in
FIG. 13, because of fluctuation of a trigger output interval of the
master node 2 (see FIG. 5) or clock fluctuation when a time slot is
periodically transmitted as shown in No. 1004 and No. 1005 of FIG.
7.
As illustrated with a CK in a left part of FIG. 13, if clocks are
matched, timing of the time slots TS1 and TS2 transmitted and
received by the nodes A to C are matched to each other. However, as
illustrated in a right part of FIG. 13 with CK1 and CK2, if timing
of a time slot is deviated because of clock fluctuation, the time
slot TS1 is overlapped with the time slot TS2 as indicated by a
two-way arrow L1.
Guard times are therefore given before and after a data as
illustrated in FIG. 14, taking into account a possible overlap of
time slots because of clock fluctuation. A guard time for a certain
period of time in a time slot (TS length) can prevent the time
slots from overlapping.
Next is described physical topology.
FIG. 15 is a block diagram illustrating an example of a
configuration of an optical switch node 1A in a unidirectional
ring. The configuration in the unidirectional ring is similar to
that explained with reference to FIG. 3 and FIG. 4, detailed
description of which is thus omitted herefrom.
FIG. 16 is a block diagram illustrating an example of an optical
switch node 1B on a bidirectional ring.
If the physical topology is bidirectional (a bidirectional ring),
two trigger detection units 21 and two TS information management
units 10 are provided, each one of which is used for clockwise, and
the other, counterclockwise. Time slots can be allocated in such a
transmission direction that communications between nodes avoid
passing through a master node, which makes it possible to set the
TS length or the TS period without depending on the ring length.
The master node transmits a trigger clockwise or counterclockwise
with respect to the ring. Based on TS information in the
information management unit 10 corresponding to transmission and
receipt directions of the trigger, each of the nodes transmits or
receives data and changes over a switch in a direction same as the
transmission and receipt directions of the trigger. If the node
receives a clockwise trigger, the node uses the clockwise time slot
information management unit 10 and appropriately transmits or
receives data and changes over a switch, and so does the
counterclockwise time slot information management unit 10.
Next are described variations of a configuration of a trigger
transmission. FIG. 17A and FIG. 17B, and FIG. 18A and FIG. 18B are
diagrams each illustrating a variation of the configuration example
of the trigger transmission.
FIG. 17A and FIG. 17B each illustrate a configuration example in a
case where a trigger is made to pass through the optical TS-SW unit
30. FIG. 18A and FIG. 18B each illustrate a configuration example
in a case where a trigger is not made to pass through the optical
TS-SW unit 30.
In the configuration example illustrated in FIG. 17A, the optical
TS-SW unit 30 is set at broadcast. The optical TS-SW unit 30
demultiplexes the trigger. In the configuration example illustrated
in FIG. 17B, the optical TS-SW unit 30 is set at DROP/ADD. The
trigger detection unit 21 demultiplexes the trigger.
In the configuration example illustrated in FIG. 18A, an electrical
signal generated by OE-EO (optical-electrical) conversion, or an
optical coupler demultiplexes the trigger. In the configuration
example illustrated in FIG. 18B, the trigger detection unit 21
demultiplexes the trigger.
Next are described variations of a configuration of connection
between the TS transmit-receive unit 40 and the optical TS-SW unit
30.
FIG. 19A to FIG. 19C are diagrams each illustrating a variation of
a configuration of connection between the TS transmit-receive unit
40 and the optical TS-SW unit 30.
FIG. 19A illustrates a configuration example in a case of one input
and one output. FIG. 19B illustrates a configuration example in a
case of one input and an output for each queue. FIG. 19C
illustrates a configuration example in a case of two inputs and an
output for each queue.
In the configuration illustrated in FIG. 19A, the TS
transmit-receive unit 40 has a plurality of queues 40q1, 40qn.
Transmitted data is stored in either of the queues according to a
destination thereof. The TS transmit-receive unit 40 is connected
to the optical TS-SW unit 30 with one port for each of
ADD/DROP.
In the configuration illustrated in FIG. 19B, the TS
transmit-receive unit 40 has a plurality of queues 40q1, 40qn. The
TS transmit-receive unit 40 is connected to the optical TS-SW unit
30 with one ADD port for each queue. Data having different
destinations can be thus outputted simultaneously if ring
transmission directions of the data are different.
In the configuration illustrated in FIG. 19C, the TS
transmit-receive unit 40 has a plurality of queues 40q1, 40qn and a
buffer 40b. The TS transmit-receive unit 40 is connected to the
optical TS-SW unit 30 also with two DROP ports. Data even
simultaneously transmitted from both sides can be thus
received.
Next is described a variation of how to supply a clock used for
counting an elapsed time in the optical SW control unit 22 and the
transmission control unit 23.
FIG. 20A and FIG. 20B are diagrams for explaining variations of how
to supply a clock.
FIG. 20A is a block diagram illustrating a configuration of an
optical switch node 1C in which an internal clock (CK3) is used for
counting an elapsed time. The internal clock (CK3) used herein may
be a cesium oscillator, a rubidium oscillator, a crystal oscillator
or the like. FIG. 20B is a block diagram illustrating a
configuration of an optical switch node 1D in which an external
clock (CK4) is used for counting an elapsed time. The external
clock (CK4) used herein may be a GPS (Global Positioning System)
clock and a JJY clock (a Japan standard radio wave clock) or the
like.
In the first embodiment, a wavelength path having a single
wavelength is divided into time slots, and the time slots are
allocated to a plurality of nodes such that the time slots are not
overlapped one another. This makes it possible to transmit or
receive data or switch a route for each node. Thus, the number of
nodes can be increased without depending on the number of
wavelength paths.
Second Embodiment
A second embodiment is configured such that time slot information
is embedded in a trigger and is delivered to a node with the
trigger embedded therein.
FIG. 21 is a block diagram illustrating a configuration example of
an optical switch node 1E according to a second embodiment. FIG. 22
is a diagram schematically illustrating transmission routes of a
control signal and an optical signal in the optical switch node 1E
illustrated in FIG. 21.
As illustrated in FIG. 21, the optical switch node 1E according to
the second embodiment does not include the TS information
management unit 10 illustrated in FIG. 3. Meanwhile, in the second
embodiment, as illustrated in FIG. 22, the trigger detection unit
21 transfers, upon receipt of a trigger, the TS information
embedded in the trigger, to the transmission control unit 23 and
the optical SW control unit 22.
FIG. 23 is a block diagram illustrating a configuration example of
a master optical switch node (a master node) 2E according to the
second embodiment. FIG. 24 is a diagram schematically illustrating
transmission routes of a control signal and an optical signal in
the master node 2E illustrated in FIG. 23.
The master node 2E according to the second embodiment has a
configuration similar to that of the master node 2 illustrated in
FIG. 5 except that, as illustrated in FIG. 23 and FIG. 24, the
master node 2E further includes a TS information delivery unit 60
that embeds the TS information in the trigger and delivers the
trigger with the TS information embedded therein.
Next are described operations of the optical network system
according to the second embodiment when the trigger output interval
is the "TS length".
FIG. 25 is a diagram for explaining operations in the optical
network system according to the second embodiment, when the trigger
output interval is the "TS length". Referring to FIG. 25, the
operations are described in a case where a data is transmitted from
node A to node B using an optical signal.
As illustrated in [1], the master node 2E writes TS information
200, 201, and 202 into a trigger and transmits the trigger at
intervals of the TS length. Information herein is assumed to be of
1 trigger 1 TS. FIG. 25 illustrates how the master node 2E
transmits three pieces of TS information having TS numbers=0 to 2,
as exemplified in the TS information 200, 201, and 202.
As illustrated in [2], upon receipt of the trigger, node A reads
the TS information in the trigger, and, if a data transmission
source or a data transmission destination is node A itself,
performs an appropriate operation corresponding to that in the TS
information after an offset time (herein, 5 counts). If the TS
information has the TS number=0, a node as a data transmission
source is the node itself. Thus, node A performs an ADD of the data
after the offset time. Upon receipt of a subsequent trigger, node A
performs an operation similarly to the described above.
As illustrated in [3], upon receipt of the trigger, node B: reads
the TS information in the trigger, and, if a data transmission
source or a data transmission destination is node B itself,
performs an appropriate operation corresponding to that in the TS
information after the offset time. That is, if the TS information
has the TS number=0, a node as a data transmission source is the
node itself. Thus node B performs DROP of the data after the offset
time. Upon receipt of a subsequent trigger, node B performs an
operation similarly to the described above.
In the second embodiment, advantageous effects similar to those in
the first embodiment can be obtained. Further, it is not necessary
to provide each of the master node 2E and the optical switch node
1E with the TS information management unit 10.
Next is described a variation in which TS synchronization is
performed not by a trigger delivered from the master node but by a
time.
How to perform the TS synchronization to be described herein is
characterized in that a TS start is specified by a time. The
synchronization by the above-described trigger requires that a
trigger and a data pass the same route. However, the TS
synchronization specified by a time allows a preliminary setting of
a TS start time, and does not require that the TS start time and a
data pass the same route even in a case of delivering the TS start
time.
When a time is set at a node, two cases can be contemplated. One is
that a time to which a delay time is added corresponding to a data
transmission path relative to a time of a master node (to be
detailed hereinafter in a third embodiment and a fourth embodiment)
is set. The other is that a time common to all nodes is set (to be
detailed hereinafter in a fifth embodiment).
When the time to which the delay time is added is set, a TS start
time can be advantageously made to be common to all nodes. When the
common time is set, the time can be set using the GPS or the
like.
Third Embodiment
An optical network system according to a third embodiment is
configured such that a time at a node is set at a time shifted by a
transmission delay time, by transmitting a time stamp from a master
node. Thus, time slots are synchronized at a time common to all
nodes, at which data transmission and receipt can be realized.
Next is described a configuration of an optical switch node
according to this embodiment.
FIG. 26 is a block diagram illustrating a configuration example of
an optical switch node 1F according to the third embodiment. FIG.
27 is a diagram schematically illustrating transmission routes of a
control signal and an optical signal in the optical switch node 1F
illustrated in FIG. 26.
As illustrated in FIG. 26, the optical switch node 1F includes a TS
information management unit 10 that sets TS information; a TS
synchronization unit 25; a time counter 70; an optical TS-SW unit
30; and a TS transmit-receive unit 40. The TS synchronization unit
25 includes; a control signal processing unit 26; a transmission
control unit 23; and an optical SW control unit 22. The optical
TS-SW unit 30 is connected to a demultiplexing unit 31 on an input
side of an optical signal and is connected to a multiplexing unit
32 on an output side of the optical signal.
Next description is made with reference to FIG. 27. The control
signal processing unit 26: detects a control signal for
synchronizing timings of time slots of nodes; notifies the time
counter 70 of a time stamp value of the signal; and also notifies
the transmission control unit 23 and the optical SW control unit 22
of a time slot start time (which may also be referred to as a TS
start time hereinafter) in the signal.
The time counter 70: sets a counter value at the time stamp value
notified by the control signal processing unit 26; and supplies the
transmission control unit 23 and the optical SW control unit 22
with the counter value.
Upon receipt of the TS start time notified by the control signal
processing unit 26, the transmission control unit 23: references
the TS information management unit 10; and, when a counter value
supplied from the time counter 70 reaches the TS start time, gives
a start instruction to the TS transmit-receive unit 40 using a time
slot allocated to the transmission control unit 23 itself.
The TS transmit-receive unit 40: stores data inputted from outside
in a buffer (not shown); transmits the data read from the buffer in
accordance with an instruction from the transmission control unit
23, to the optical TS-SW unit 30; and transmits the data received
from the optical TS-SW unit 30, to outside.
Upon receipt of the TS start time notified by the control signal
processing unit 26, the optical SW control unit 22: references the
TS information management unit 10; and instructs the optical TS-SW
unit 30 to switch routes at a time slot allocated to the optical SW
control unit 22 itself, when the counter value supplied from the
time counter 70 indicates the TS start time.
The optical TS-SW unit 30 switches routes under the switching
instruction from the optical SW control unit 22.
Next is described a configuration of a master optical switch node
according to the third embodiment.
FIG. 28 is a block diagram illustrating a configuration example of
a master optical switch node (a master node) 2F according to the
third embodiment. FIG. 29 is a diagram schematically illustrating
transmission routes of a control signal and an optical signal in
the master node 2F illustrated in FIG. 28.
As illustrated in FIG. 28, the master node 2F includes: a TS start
delivery unit 80; and a delay time calculation unit 90, in addition
to the configuration described with reference to FIG. 26. The TS
start delivery unit 80 includes: a control signal generation unit
81; and a master time counter 82.
Next description is made with reference to FIG. 29. The master time
counter 82 supplies the control signal generation unit 81 with a
counter value.
The control signal generation unit 81: generates a control signal
containing a TS start time; adds the counter value supplied from
the master time counter 82 as a time stamp, to the control signal;
and transmits the control signal to the node 1F.
The delay time calculation unit 90 subtracts the time stamp value
from a time when the control signal after making one round of a
ring is received; calculates a time required for one round of the
ring; and writes a result of the calculation to the TS information
management unit 10.
Operations of the optical network system according to the third
embodiment are similar to those according to a fourth embodiment to
be described hereinafter, detailed description of which is thus
omitted herefrom.
In the third embodiment, a time at each of the nodes 1F is set at a
time shifted by a transmission delay time, by transmitting a time
stamp from the master node 2F. Thus, time slots are synchronized at
a time common to all the nodes 1F, at which data transmission and
receipt can be realized.
Fourth Embodiment
A fourth embodiment is configured such that, in the optical network
system according to the third embodiment, a master node delivers TS
information to each of nodes.
FIG. 30 is a block diagram illustrating a configuration example of
an optical switch node 1G according to the fourth embodiment. FIG.
31 is a diagram schematically illustrating transmission routes of a
control signal and an optical signal in the optical switch node 1G
illustrated in FIG. 30. As illustrated in FIG. 30, the optical
switch node 1G in this embodiment is similar to the optical switch
node 1F illustrated in FIG. 26, except that the optical switch node
1G does not include the TS information management unit 10.
FIG. 32 is a block diagram illustrating a configuration example of
a master optical switch node (a master node) 2G according to the
fourth embodiment. FIG. 33 is a diagram schematically illustrating
transmission routes of a control signal and an optical signal in
the master node 2G illustrated in FIG. 32.
Compared to the configuration illustrated in FIG. 28, as
illustrated in FIG. 32, the master node 2G includes the TS
information delivery unit 60 that supplies the control signal
generation unit 81 with the TS information, though not including
the TS information management unit 10.
In the optical network system configured as described above, a
variation is described in a case where a time is utilized with a TS
start delivery function and a TS synchronization function, and a
time counter is set at a time with a delay difference added
thereto.
FIG. 34 is a diagram illustrating a variation in the case where a
time is utilized with a TS start delivery function and a TS
synchronization function, and a time counter is set at a time with
a delay difference added thereto. As illustrated in a lower part of
FIG. 34, as a control signal for use in setting the TS information,
a plurality of pieces of information may be put together and
contained into a control signal SS, and then transmitted.
Alternatively, a plurality of pieces of the information may be
separated and contained into control signals SS1, SS2, SS3, and
then transmitted. That is, the control signal SS contains a TS
start time, a time stamp, and the TS information all together.
Meanwhile, the control signal SS1 contains the TS start time, the
control signal SS2 contains the time stamp, and the control signal
SS3 contains the TS information.
Next are described operations of the optical network system
according to the fourth embodiment.
FIG. 35 is a diagram for explaining operations of No. 2002
illustrated in FIG. 34. Referring to FIG. 35, next is described a
case where a local time and a TS start time are delivered, and
setting to all TSs is previously performed.
As illustrated in [1] and [2], the master node 2G sets time slot
information to nodes A, B. Then, as illustrated in [3], the master
node 2G transmits a control signal SS4 containing the TS start time
and a time stamp value (for example, 80) for each TS period.
As illustrated in [4], upon receipt of the control signal SS4 from
the master node 2G, node A sets the time stamp value (80) at a time
counter (80). As illustrated in [5], when the time counter reaches
the TS start time (100), node A sequentially performs operations
starting from TS0. That is, node A performs operations of the TS
information, when a time of "TS start time+TS number.times.TS
length" is reached. Herein, as illustrated in line 1 of [1], node A
performs an ADD of a data to TS0 at 100 to 120 of the time counter,
and performs an ADD of the data to TS2 at 140 to 160 of the time
counter.
As illustrated in [6], upon receipt of the control signal SS4, node
B sets a time stamp value at the time counter (80). When the time
counter reaches the TS start time (100), node B sequentially
performs appropriate operations starting from TS0. That is, as
illustrated in line 1 of [2], node B: performs a DROP of a data of
TS0 at 100 to 120 of the time counter (=TS start time+TS
number.times.TS length); and, as illustrated in the second line of
[2], performs an ADD of the data to TS2 at of the time counter 120
to 140.
Next is described how to set a time to which a transmission path
delay time is added.
FIG. 36A and FIG. 36B are diagrams each for explaining how to set
the time to which the transmission path delay time is added.
As illustrated in FIG. 36A, the master node 2G transmits a time
synchronization signal with a time stamp, as illustrated in a box
G1. Each of the optical switch nodes 1G sets a time stamp value of
the received time synchronization signal at a current time as
illustrated in a box G2.
As illustrated in FIG. 36B, in the master node 2G, a time (T1) when
the time synchronization signal is transmitted is given as a time
stamp. A time synchronization signal SC1 to which the time stamp
value T1 is given is transmitted to each of the optical switch
nodes 1G. In each of the optical switch nodes 1G, the value (T1) of
the time stamp is set as a current time of each of the optical
switch node 1G itself.
As described above, the master node 2G transmits the time
synchronization signal SC1 with the time stamp to the optical
switch node 1G, based on which the time to which a transmission
path delay time is added is set. Periodic transmissions of the time
synchronization signal SC1 make it possible to absorb a change in a
transmission path length owing to temperature fluctuation.
Next is described a variation of how to set a time with delay.
FIG. 37A and FIG. 37B are diagrams each for explaining a variation
of how to set a time with delay. FIG. 37A illustrates a case where
a time stamp transmission direction is counterclockwise as
indicated by an arrow Y1. FIG. 37B illustrates a case where the
time stamp transmission direction is clockwise as indicated by an
arrow Y2.
In a case of a unidirectional setting, the master node 2G:
transmits a control signal with a time stamp either
counterclockwise illustrated in FIG. 37A or clockwise illustrated
in FIG. 37B; and sets an appropriate time with delay to each of
nodes 1G1, 1G2, 1G3.
Description herein is made by exemplifying a counterclockwise case,
as illustrated in FIG. 37A. Assume that the master node 2G makes a
local time t as a time stamp value and transmits the time stamp by
containing in a control signal, which is received by node 1G1. In
this case, let "a" be a transmission delay between the master node
2G and the node 1G1. The node 1G1 sets the time stamp value "t" of
the control signal as a local time in the time counter of its own
node 1G1. At this time, a local time of the master node 2G advances
by a delay time "a". The local time of the node 1G1 is thus set at
a time (t-a) which is a time shifted from the local time of the
master node 2G by the delay time a.
Similarly, a local time of a subsequent node 1G2 is set at "t". The
local time of the node 1G2 is thus set at a time (t-a-b) which is a
time shifted from the local time of the master node 2G by a delay
time (a+b). The local time of a node 1G3 is set at "t". The local
time of the node 1G3 is thus set at a time (t-a-b-c) shifted from
the local time of the master node 2G by a delay time (a+b+c).
In a case of a bidirectional setting, the master node 2G transmits
a control signal with a time stamp to each of the nodes 1G1 to 1G3,
both counterclockwise illustrated in FIG. 37A and clockwise
illustrated in FIG. 37B. As illustrated in FIG. 37A and FIG. 37B,
different local times are set when the time stamp value is
transmitted clockwise and counterclockwise. Each of the nodes 1G1
to 1G3 may thus have a pair of time counters, one used for
clockwise and the other used for counterclockwise.
Next is described a variation of physical topology.
FIG. 38 is a block diagram illustrating a configuration example of
an optical switch node 1H in a case of a unidirectional ring. The
configuration in the case of the unidirectional ring is similar to
that described with reference to FIG. 26 and FIG. 27, detailed
description of which is thus omitted herefrom.
FIG. 39A and FIG. 39B are block diagrams illustrating examples of
configurations of optical switch nodes 1I, 2J on bidirectional
rings, respectively. Note that the optical switch node 1I
illustrated in FIG. 39A is applied also as a master node 2I to be
described hereinafter.
In a case where the physical topology is bidirectional illustrated
in FIG. 39A, two control signal processing units 26, two TS
information management units 10, and two time counters 70 are
provided, each one of which is used for clockwise, and the other,
for counterclockwise. The master node 2I transmits a control signal
onto a ring both clockwise and counterclockwise. Each of the nodes
1I operates using TS information in the TS information in one of
the management units 10 and one of the time counters 70, which
correspond to a transmission and receipt direction of the control
signal. Upon receipt of a clockwise control signal, each of the
nodes 1I uses the clockwise TS information management unit 10 and
the clockwise time counter 70.
In a case where physical topology is bidirectional as illustrated
in FIG. 39B, the control signal processing units 26, the TS
information management units 10, and the time counters 70 together
perform a bidirectional communication as a set. Note that FIG. 39B
illustrates a configuration of the master node 2J. The master node
2J transmits a control signal on a ring clockwise or
counterclockwise. If the master node 2J transmits data in a
direction opposite to the transmission and receipt direction of the
control signal, the master node 2J operates with a time obtained by
subtracting a delay time from the TS start time by the delay time
calculation unit 90. When the master node 2J transmits a data in a
direction same as a receipt direction of the control signal, a
method same as that of the unidirectional ring is performed.
Next is described a DROP switching time of a master node.
FIG. 40 is a diagram for explaining a DROP switching time of the
master node 2J.
As described above with reference to FIG. 37A and FIG. 37B, the
local times with respective differences from that of the master
node 2J by delays are set to the nodes 1J1 to 1J3. Therefore, if a
data is transmitted in a direction same as that of transmitting
a time stamp, "Reception time of receiving node at local
time"="Transmission time of transmitting node at local time". For
example, if the master node 2J transmits a data at the local
time=t1, the data arrives at the nodes 1J1 to 1J3 at respective
local times=t1.
On the other hand, when the nodes 1J1 to 1J3 transmit data to the
master node 2J or transmit or receive data between the nodes 1J1 to
1J3 jumping over the master node 2J, "Reception time of receiving
node at local time"="Transmission time of transmitting node at
local time"+"Ring one-round time (a+b+c+d)".
The data transmission and reception jumping over the master node 2J
(which may also be referred to as a jump communication) used herein
means that, in a forward direction of transmission, a signal
transmitted from the node 1J3 connected upstream of the master node
2J skips (jumps over) the master node 2J is received by the node
1J1 connected downstream of the master node 2J or a further
downstream node. In a backward direction of the transmission, a
signal transmitted from the node 1J1 connected downstream of the
master node 2J skips (jumps over) the master node 2J is received by
the node 1J3 connected upstream of the master node 2J or a further
upstream node.
For example, when the node 1J1 transmits a data at a local time=t2,
the data arrives at the master node 2J at a local time=t2+a+b+c+d
of the master node 2J. Therefore, a DROP switching time of the
master node 2J is calculated by "TS start time+TS number.times.TS
length+Ring one-round time". Similarly, the DROP switching time of
transmitting or receiving data jumping over the master node 2J, as
in a case of transmitting or receiving a data from the node 1J3 to
the node 1J1, is calculated by "TS start time+TS number.times.TS
length+Ring one round time".
FIG. 41 is a diagram illustrating an example of setting TS
information of a master node.
As illustrated in FIG. 41, in order to handle a case in which
"Reception time=Transmission time" is not satisfied, a ring
one-round time (a+b+c+d) is taken into account. A time when the
master node 2J performs a DROP is calculated by "TS start time+TS
number.times.TS length+Ring one-round time".
Next is described how to calculate and set a ring one-round time.
Two methods are explained herein.
Method 1 is that a delay time is previously measured using a
measuring instrument such as an OTDR, and a result of the
measurement is set to the TS information management unit 10. The
setting to the TS information management unit 10 may be performed
manually or the like.
Method 2 is that the ring one-round time is calculated from a
control signal having been made one round of a ring. Method 2 is
described with reference to FIG. 42. FIG. 42 is a diagram for
explaining how to calculate and set the ring one-round time.
As illustrated in FIG. 42, the control signal generation unit 81 of
a master node 2K generates a control signal SS10 with a time stamp
and transmits the generated control signal SS10. The delay time
calculation unit 90 of the master node 2K: receives the control
signal SS10 with the time stamp which has been returned after
making one round of the ring; calculates a ring one-round time by
subtracting a time stamp value from a receipt time; and writes the
calculated ring one-round time to the TS information management
unit 10.
FIG. 43 is a diagram illustrating variations each in a case where a
time counter is set at a common time. In this embodiment, because
the common time is set, it is not necessary to deliver a signal for
setting a local time of each node.
Fifth Embodiment
A fifth embodiment is configured such that each of nodes shares
information on a common time, measures a delay time, and performs a
TS synchronization by subtracting a delay time from a TS start
time.
Next is described a configuration of an optical switch node
according to the fifth embodiment.
FIG. 44 is a block diagram illustrating a configuration example of
an optical switch node 1L according to the fifth embodiment. FIG.
45 is a diagram schematically illustrating transmission routes of a
control signal and an optical signal in the optical switch node 1L
illustrated in FIG. 44.
As illustrated in FIG. 44, the optical switch node 1L includes: a
TS information management unit 10 that sets TS information; a TS
synchronization unit 25; a common time counter 75; a delay time
management unit 95; an optical TS-SW unit 30; and a TS
transmit-receive unit 40. The TS synchronization unit 25 includes:
a control signal processing unit 26; a transmission control unit
23; and an optical SW control unit 22. The optical TS-SW unit 30 is
connected to the demultiplexing unit 31 on an input side of an
optical signal and is connected to the multiplexing unit 32 on an
output side of the optical signal.
Next description is made with reference to FIG. 45. Upon receipt of
a control signal, the control signal processing unit 26 notifies
the transmission control unit 23 and the optical SW control unit 22
of a TS start time. If the control signal contains TS information,
the control signal processing unit 26 writes the TS information to
the TS information management unit 10.
The TS information management unit 10: manages the TS information;
and makes the transmission control unit 23 and the optical SW
control unit 22 reference the TS information. The TS information
includes information on a TS number, a data transmission
destination, an operation, an optical SW connection port number, a
TS length, and a TS period.
Upon receipt of the notification of the TS start time from the
control signal processing unit 26, the transmission control unit
23: references the TS information management unit 10 and the delay
time management unit 95; and performs an operation having a
corresponding TS number. If the operation is an ADD, the
transmission control unit 23 instructs the TS transmit-receive unit
40 to transmit a data to an appropriate data transmission
destination. The common time counter 75 supplies the transmission
control unit 23 with a time.
The TS transmit-receive unit 40 transmits or receives data between
an external unit (not shown) and the optical TS-SW unit 30. The
external unit is, for example, a communication device such as the
routers or the like illustrated in FIG. 1. When the TS
transmit-receive unit 40 transmits data to another optical switch
node via the optical TS-SW unit 30, the TS transmit-receive unit
40: reads, under a transmission instruction from the transmission
control unit 23, an appropriate data from a queue in the buffer
(not shown) such that the another optical switch node becomes a
destination; and transfers the data to the optical TS-SW unit 30.
Upon receipt of the data from the external unit, the TS
transmit-receive unit 40 holds the data in the queue in the buffer
until the transmission control unit 23 instructs the
transmission.
Upon receipt of the notification of the TS start time from the
control signal processing unit 26, the optical SW control unit 22:
references the TS information management unit 10 and the delay time
management unit 95; and performs an operation having corresponding
TS number. If the corresponding operation is an ADD or a DROP, the
optical SW control unit 22 instructs the optical TS-SW unit 30 to
perform a switching. After a time corresponding to the TS length
elapses from the instruction of the switching, the optical SW
control unit 22 instructs the optical TS-SW unit 30 to perform a
switching back. The common time counter 75 supplies the optical SW
control unit 22 with a time.
The optical TS-SW unit 30 switches a connection in the optical SW
under the switching instruction from the optical SW control unit
22.
The common time counter 75: is supplied with a clock (not shown);
and counts a time. The time is shared by all the nodes.
The delay time management unit 95 manages delay times of the master
node and of its own.
Next is described a configuration of a master optical switch node
(a master node) according to this embodiment.
FIG. 46 is a block diagram illustrating a configuration example of
a master node 2L according to this embodiment. FIG. 47 is a diagram
schematically illustrating transmission routes of a control signal
and an optical signal in the master node 2L illustrated in FIG.
46.
As illustrated in FIG. 46 and FIG. 47, a configuration of the
master node 2L is similar to that explained with reference to FIG.
44 except that the master node 2L includes the control signal
generation unit 81, instead of including the delay time management
unit 95. The control signal generation unit 81: generates a control
signal containing a TS start time and a time stamp; and transmits
the generated control signal to each of the nodes.
FIG. 48 is a diagram illustrating a configuration example of an
optical network system according to the fifth embodiment. The
master node 2L illustrated in FIG. 48 corresponds to the master
node 2L illustrated in FIG. 46. Nodes 1L1 to 1L5 correspond to the
optical switch node 1L illustrated in FIG. 46. In this
configuration, the master node 2L transmits a control signal SS11
and a data D11 in a counterclockwise direction indicated by an
arrow Y3.
Next is described a TS start time in a case where a common time is
set.
FIG. 49A is a configuration of an optical network system in which
the master node 2L and two nodes 1L1, 1L2 are ring-connected. FIG.
49B is a diagram for explaining a TS start time in a case where a
common time is set in the optical network system.
As illustrated in FIG. 49B, let "t" be a TS start time at which the
master node 2L transmits. Then, the nodes 1L1, 1L2 add delay times
"a" and "a+b" from the master node 2L, to the transmitted TS start
time t, respectively, to thereby update the respective TS start
times.
Further description is made with reference to FIG. 49A. At the
master node 2L, a counterclockwise delay time indicated by an arrow
Y4.apprxeq.0, and a clockwise delay time indicated by an arrow
Y5.apprxeq.0 (the delay times are extremely small and are thus
regarded as 0). Meanwhile, at the node 1L1, a counterclockwise
delay time from the master node 2L=a, and a clockwise delay time
therefrom=b+c. At the node 1L2, a counterclockwise delay time from
the master node 2L=a+b, and a clockwise delay time=c.
Next is described how to measure a delay time.
FIG. 50 is a diagram for explaining how to measure a delay time.
FIG. 50 illustrates a configuration of only a functional block
relevant to how to measure a delay time of each of the master node
2M and the optical switch node 1M, configurations of the other
functional blocks of which are omitted herefrom.
A delay time is measured by transmitting and receiving a time stamp
as described below.
Firstly, the time stamp transmission unit 81m of the master node 2M
transmits a time stamp. In a case of a bidirectional ring, the time
stamp is transmitted in both directions. Upon receipt of the time
stamp, the time stamp processing unit 26m of the optical switch
node 1M calculates a delay time by subtracting a time stamp value
from a receipt time. The time stamp processing unit 26m writes a
result of the calculation to the delay time management unit 95. The
delay time can be calculated by "Delay time=Receipt time-Time stamp
value". The delay time management unit 95 manages both ring
clockwise and counterclockwise delay times.
Next is described a specific example of configurations of optical
TS-SW units of the master node 2M and the optical switch node 1M in
the above-described embodiment.
FIG. 51 is a diagram classifying optical TS-SW units applicable to
the above-described embodiment.
The optical TS-SW unit: accommodates a data line in a ring network;
and changes a connection relation between an input port and an
output port under an instruction from a scheduler. The data line
accommodated is grouped into two cases: [1] a
wavelength-multiplexed data line; and [2] a
non-wavelength-multiplexed data line. The optical TS-SW unit used
herein is assumed to be a switch of wavelength routing type using
wavelength conversion, a spatial switch of broadcast and select
type, or the like.
More specifically, in accommodating a wavelength multiplexed data
line, as illustrated in [1], a demultiplexing unit: is provided
before the optical TS-SW unit inputs a data; demultiplexes the data
inputted through wavelength multiplexing into, for example, n
wavelengths; and gives the demultiplexed wavelengths to each of
input ports IN 1 to IN N. Then, a multiplexing unit: is provided in
a subsequent stage of the optical TS-SW unit; multiplexes N optical
signals from each of the N output ports OUT 1 to OUT N of the
optical TS-SW unit; and transmits the multiplexed optical signal to
a subsequent node in the ring network (a node in a subsequent
stage). The optical TS-SW unit: also has functions of inserting an
optical signal (ADD) and branching an optical signal (DROP); and is
thus equipped with a port for ADD as an input port thereof, and a
port for DROP as an output port thereof.
In accommodating a data line not wavelength multiplexed, as
illustrated in [2], neither a demultiplexing unit nor a
multiplexing unit is provided. In this case, the number of data
lines on a ring is the same as that of terminals (ports) from which
the number of interfaces is subtracted.
Next are described Examples 1 to 8 of the wavelength routing
switch.
Note that Examples 1 to 5 each describe a configuration example of
an optical TS-SW unit which does not include a FWC (fixed
wavelength converter). While on the other hand, Examples 6 to 8
each describe a configuration example of an optical TS-SW unit
which includes a FWC. In each of figures of Examples 1 to 8, in
order to distinguish an operation (DROP and the like) corresponding
to a signal at wavelength .lamda., an alphabetical suffix is added
to a numeric character of the wavelength .lamda..
Example 1
Next is described a configuration of an optical TS-SW unit
according to Example 1. A case of a double ring, 1 ADD/1 DROP, and
inter-fiber exchangeability is assumed herein.
FIG. 52 is a diagram for explaining a configuration of an optical
TS-SW unit 30A according to Example 1.
The optical TS-SW unit 30A includes: a kN.times.kN circular AWG
(Arrayed Waveguide Grating) 30a in which, with respect to kN
wavelengths of .lamda.i (i=0 to kN-1), a plurality of wavelengths
whose "i MOD N" take the same value are deemed as the same
wavelengths; k units of circular 1.times.N AWGs 30b, 30c; k(N-2)
units of THRU (passing through)/DROP TWC 1 to TWC 4 that are
disposed at a prior stage of the AWG 30a and serve as a wavelength
conversion unit and a demultiplexing unit, respectively; one unit
of ADD TWC [A]; one optical receiver 30e as a DROP interface; and k
units of (N-1).times.1 multiplexing units 30x, 30y. FIG. 52
illustrates a case wherein k=2 and N=4.
Herein, the TWC is a variable wavelength converter. The circular
AWG (which may also be simply referred to as an AWG) 30a
distributes an optical signal inputted in an input port into an
appropriate output port according to a wavelength thereof. That is,
the optical TS-SW unit 30A exemplifies a case in which a double
ring and 4 wavelengths for each ring are used, and also in which
inter-fiber wavelength exchange is performed with a configuration
of 1 ADD/1 DROP without using FWCs.
Example 2
Next is described a configuration of an optical TS-SW unit
according to Example 2. A case of a double ring, 1 ADD/1 DROP,
inter-fiber exchangeability, and a wavelength for switch control is
assumed herein.
FIG. 53 is a diagram for explaining a configuration of an optical
TS-SW unit 30B according to Example 2.
The optical TS-SW unit 30B includes: the kN.times.kN circular AWG
30a in which, with respect to kN wavelengths of .lamda.i (i=0 to
kN-1), a plurality of wavelengths whose "i MOD N" take the same
value are deemed as the same wavelengths; k units of the circular
1.times.N AWGs 30b, 30c that are disposed at the prior stage of the
AWG 30a and serve as a wavelength conversion unit and a
demultiplexing unit; k(N-2) units of the THRU (passing
through)/DROP TWC 1 to TWC 4; one unit of ADD TWC [A]; the optical
receiver 30e as a DROP interface; and k units of the (N-1).times.1
multiplexing units 30x, 30y. Further, a wavelength for control is
prepared for performing a switch control. The demultiplexing units
30b, 30c are connected to the couplers 30f, 30g, respectively, so
as to ensure reachability of the wavelength for control. Each of
switches performs a copy operation. FIG. 53 illustrates a case
where k=2 and N=4.
That is, the optical TS-SW unit 30B exemplifies a case: in which a
double ring and 4 wavelengths for each ring are used; in which
inter-fiber wavelength exchange is performed with a configuration
of 1 ADD/1 DROP without using FWCs; and in which a wavelength for
control is further used.
Example 3
Next is described a configuration of an optical TS-SW unit
according to Example 3. A case of a double ring, 1 ADD/1 DROP, and
inter-fiber exchangeability is assumed herein.
FIG. 54 is a diagram for explaining an optical TS-SW unit 30C
according to Example 3.
The optical TS-SW unit 30C includes: the kN.times.kN circular AWG
30a in which, with respect to kN wavelengths of .lamda.i (i=0 to
kN-1), a plurality of wavelengths whose "i MOD N" take the same
value are deemed as the same wavelengths; k units of the circular 1
.thrfore.N AWGs 30b, 30c that are disposed at the prior stage of
the AWG 30a and serve as a wavelength conversion unit and a
demultiplexing unit; k(N-2) units of the THRU (passing
through)/DROP TWC 1 to TWC 4; one unit of ADD TWC [A] and a
demultiplexing unit 30j that are disposed at a subsequent stage of
the AWG 30a; the optical receiver 30e as a DROP interface; and k
units of the (N-1).times.1 multiplexing units 30x, 30y. FIG. 54
illustrates a case where k=2 and N=4.
That is, the optical TS-SW unit 30C exemplifies a case: in which a
double ring and 4 wavelengths for each ring are used; and in which
inter-fiber wavelength exchange is performed with a configuration
of 1 ADD/1 DROP without using FWCs.
Example 4
Next is described a configuration of an optical TS-SW unit
according to Example 4. A case where both inter-fiber exchange and
in-fiber exchange are possible is assumed herein.
FIG. 55 is a diagram for explaining an optical TS-SW unit 30D
according to Example 4.
The optical TS-SW unit 30D includes: the kN.times.kN circular AWG
30a in which, with respect to kN wavelengths of .lamda.i (i=0 to
kN-1), a plurality of wavelengths whose "i MOD N" take the same
value are deemed as the same wavelengths; k units of the circular
1.times.N AWGs 30b, 30c that are disposed at the prior stage of the
AWG 30a and serve as a wavelength conversion unit and a
demultiplexing unit; 1.times.N couplers (multiplexing units) 30j,
30l that are disposed at the subsequent stage of the circular AWG
30a; and k output ports 30r, 30s.
The optical TS-SW unit 30D exemplifies a case: in which a double
ring and 4 wavelengths for each ring are used; and in which
inter-fiber wavelength exchange and in-fiber wavelength exchange
can be performed without using FWCs.
Example 5
Next is described a configuration of an optical TS-SW unit
according to Example 5. A case of a double ring, 1 ADD/1 DROP, 1
AWG/1 fiber, and a wavelength for switch control is assumed
herein.
FIG. 56 is a diagram for explaining a configuration of an optical
TS-SW unit 30E according to Example 5.
The optical TS-SW unit 30E includes: kN.times.kN circular AWGs 30t,
30u in which, with respect to kN wavelengths of .lamda.i (i=0 to
kN-1), a plurality of wavelengths whose "i MOD N" take the same
value are deemed as the same wavelengths; k units of the circular
1.times.N AWGs 30b, 30c that are disposed at a prior stage of the
AWG 30a and serve as a wavelength conversion unit and a
demultiplexing unit; k(N-2) units of the THRU/DROP TWC 1 to TWC 4;
one unit of the ADD TWC [A]; the optical receiver 30e as a DROP
interface; a TWC [A/D] for inter-fiber ADD/DROP; and k units of the
(N-1).times.1 multiplexing units 30x, 30y. Further, a wavelength
for control is prepared for performing a switch control. The
demultiplexing units 30b, 30c are connected to the couplers 30f,
30g, respectively, so as to ensure reachability of the wavelength
for control. Each of switches performs a copy operation.
FIG. 56 illustrates a case where k=2 and N=4. A wavelength for data
is 2 wavelength/fiber and a wavelength for control is 1
wavelength/fiber. That is, the optical TS-SW unit 30E exemplifies a
case: in which a double ring and 4 wavelengths for each ring are
used with 1 fiber for each of the AWGs 30t, 30u; and in which a
wavelength for control is used with a configuration of 1 ADD/1 DROP
without using FWCs.
Example 6
Next is described an optical TS-SW unit according to Example 6. A
case of a double ring (1 ring 4 wavelengths) and ADD/DROP 1 CH
(channel) is assumed herein.
FIG. 57A is a diagram for explaining a configuration of an optical
TS-SW unit 30F according to Example 6. FIG. 57B is a diagram
illustrating TWC wavelength requirements between eight TWCs,
namely, TWC 1 to TWC 8, and a TWC [A] for ADD in the optical TS-SW
unit 30F.
As illustrated in FIG. 57A, the optical TS-SW unit 30F includes: a
9.times.9 AWG 30v; eight TWCs disposed at a prior stage of the
9.times.9 AWG 30v, namely, TWC 1 to TWC 8; eight FWCs disposed at a
subsequent stage of 9.times.9 AWG 30v, namely, FWC 1 to FWC 4+FWC 1
to FWC 4; and a TWC [A] for ADD. In FIG. 57A and FIG. 57B: let "r"
be a suffix of a wavelength for THRU; "g", for DROP; and "b", for
ADD, so as to distinguish one wavelength from another.
The ADD used herein means that a signal inputted in IN1 of the AWG
30v is outputted to any one of OUT1 to OUT9. The DROP used herein
means that a signal inputted in any one of IN2 to IN9 of the AWG
30v is outputted to OUT9. The THRU used herein means that a signal
inputted in any one of IN2 to IN9 of the AWG 30v is outputted to
OUT having a number obtained by subtracting 1 from the number of IN
in which the signal is inputted.
Next are described detailed operations with reference to FIG. 57A.
In a case of ADD, according to which one of OUT1 to OUT8 a signal
is outputted, TWC [A] converts a wavelength of the signal to one of
.lamda.1b to 8b and then inputs the signal into IN1. Each
wavelength inputted into IN1 corresponds to an output destination,
such as .lamda.1b to OUT1, .lamda.2b to OUT2, .lamda.3b to OUT3,
.lamda.4b to OUT4, .lamda.5b to OUT5, .lamda.6b to OUT6, .lamda.7b
to OUT7, and .lamda.8b to OUT8. Incoming signals from Fiber 1 and
Fiber 2 are demultiplexed at the AWG 30b, 30c, respectively, and
are wavelength-converted appropriately by the TWCs 1 to 8 depending
on being subjected to THRU or DROP. Correspondence between the
wavelength and the output destination is, by taking the TWC 1 as an
example, in a case of a THRU, .lamda.1 g, and .lamda.2r corresponds
to OUT1.
Example 7
Next is described a configuration of an optical TS-SW unit
according to Example 7. A case of a double ring (1 ring 4
wavelengths), ADD/DROP 1CH, and in-fiber wavelength exchange is
assumed herein.
FIG. 58A is a diagram for explaining an optical TS-SW unit 30G
according to Example 7. FIG. 58B is a diagram illustrating TWC
wavelength requirements of eight TWCs, TWC 1 to TWC 8, and the TWC
[A] for Add in the optical TS-SW unit 30G.
The optical TS-SW unit 30G illustrated in FIG. 58A has a
configuration same as that of the optical TS-SW unit 30F
illustrated in FIG. 57A except that the wavelength requirements of
the TWCs 1 to 8, and [A] are different, detailed description of
which is thus omitted herefrom. In FIG. 58A and FIG. 58B, let "r"
be a suffix of a wavelength for THRU; "g", for DROP; "b", for ADD;
and "y", for in-fiber exchange, so as to distinguish one wavelength
from another.
The in-fiber exchange herein means that, for example: a signal
inputted in any one of IN2 to IN5 of the AWG 30v is outputted to
any output destination other than OUT1 to OUT 4 for THRU; and that
a signal inputted in IN6 to IN9 of the AWG 30v is outputted to any
output destination other than OUT5 to OUT8 for THRU. Next are
described detailed operations with reference to FIG. 58A and FIG.
58B. The operations herein are similar to those of Example 6 in the
cases of ADD, DROP, and THRU. A case of the in-fiber exchange is
thus described taking the TWC 1 as an example. In a case where an
output destination of a signal inputted into IN2 of the AWG 30v is
changed to OUT2, a wavelength of the signal inputted into the TWC 1
is changed to .lamda.3y. Similarly, when the output destination is
changed to OUT3, .lamda.4y; and, to OUT4, .lamda.5y.
Example 8
Next is described a configuration of an optical TS-SW unit
according to Example 8. A case of a double ring (1 ring 4
wavelengths), ADD/DROP 1 CH, inter-fiber and in-fiber wavelength
exchange is assumed herein.
FIG. 59A is a diagram for explaining a configuration of an optical
TS-SW unit 30H of Example 8. FIG. 59B is a diagram illustrating TWC
wavelength requirements of eight TWC 1 to TWC 8 and a TWC [A] for
ADD in the optical TS-SW unit 30H.
The optical TS-SW unit 30H has a configuration similar to that of
the optical TS-SW unit 30F illustrated in FIG. 57A except that the
wavelength requirements of TWCs 1 to 8, and [A] are different,
detailed description of which is thus omitted herefrom. In FIG. 59A
and FIG. 59B, let "r" be a suffix of a wavelength for THRU; "g",
for DROP; "b", for ADD; "y", for in-fiber exchange; and "p", for
inter-fiber exchange, so as to distinguish one wavelength from
another.
The inter-fiber exchange used herein means that: a signal inputted
in any one of IN2 to IN5 of the AWG 30v is outputted to any one of
OUT5 to OUT8; and that a signal inputted in IN6 to IN9 of the AWG
30v is outputted to any one of OUT1 to OUT 4. Next are described
detailed operations with reference to FIG. 59A and FIG. 59B. The
operations herein are similar to those of Example 7 in the cases of
ADD, DROP, THRU, and in-fiber exchange. A case of the inter-fiber
exchange is thus described taking the TWC 1 as an example. In a
case where an output destination of a signal inputted into IN2 of
the AWG 30v is changed to OUT5, a wavelength of the signal inputted
into the TWC 1 is changed to .lamda.6p. Similarly, when the output
destination is changed to OUT6, .lamda.7p; to OUT7, .lamda.8p; and,
to OUT8, .lamda.9p.
Next are described configurations of a TWC and a FWC.
FIG. 60 is a block diagram illustrating a configuration example of
an optical TS-SW unit 30J including TWCs and FWCs.
The optical TS-SW unit 30J includes: a demultiplexer
(demultiplexing unit) 30b that has one or more input ports and a
plurality of output ports and demultiplexes an inputted optical
signal having been wavelength multiplexed, for each wavelength; the
AWG 30a that allocates an optical signal inputted in an input port
to an output port according to a wavelength of the optical signal;
TWC [A]1 to TWC [A]3, and TWC 1 to TWC 8 that perform wavelength
conversion so as to select from among passing through (THRU),
insertion (ADD), and branching (DROP) at an optical switch node; a
multiplexer (multiplexing unit) 30x that wavelength multiplexes an
outputted optical signal of each wavelength so as to transmit to a
subsequent stage; FWC 1 to FWC 8 that perform wavelength conversion
such that an optical signal is outputted to the same port at a
demultiplexing unit (not shown) at the subsequent stage; and an
optical receiver 30e that receives an optical signal which is
branched (DROP) at the AWG 30a.
As seen in the figure, an optical signal having been transmitted
from the subsequent stage by means of wavelength multiplexing is
demultiplexed into wavelengths .lamda.1 to .lamda.8 by the
demultiplexer 30b. The demultiplexed optical signals are inputted
into the input port of the AWG 30a via TWC 1 to TWC 8. Separately
from those signals, an optical signal to be inserted is inputted
into the input port of the AWG 30a via TWC [A]1 to TWC [A]3. Eight
of the output ports of the AWG 30a is used for transmission to the
subsequent stage. An optical signal from any of the output ports is
inputted into the multiplexer (multiplexing unit) 30x via FWC 1 to
FWC 8 and is then wavelength multiplexed and transmitted to the
subsequent step.
The AWG 30a also has the output ports each of which is used for
branching (DROP). The output port is connected to the optical
receiver 30e. The optical receiver 30e includes: a photoelectric
device (APD) that performs photoelectric conversion; a limiting
amplifier (LIM) that absorbs power differences between optical
signals; and a clock data recovery circuit (CDR) that absorbs power
differences between optical signals, which are connected in series
in this order. The optical receiver 30e absorbs power/phase
differences between signals and receives an optical signal.
In the example illustrated in FIG. 60, a wavelength .lamda.8 is
designed to be a fixed wavelength for control. One channel of each
of ADD and DROP is also designed to be for control and is connected
to a switch control unit 30k for controlling the optical TS-SW unit
30J. The switch control unit 30k also includes: an APD; a LIM; and
a CDR.
FIG. 61 is a block diagram illustrating a configuration example of
the TWC 1 to TWC 8 (or the TWC [A]1 to TWC [A]3) illustrated in
FIG. 60.
As illustrated in FIG. 61, the TWC includes: an optical burst
receiver 301; a variable wavelength light source 302a; and a
modulator 303a. The optical burst receiver 301 includes: an APD; a
LIM; and a CDR. In FIG. 61, a transmission path of an optical
signal is indicated by a solid line, and a transmission path of an
electrical signal is indicated by a broken line.
The APD performs photoelectric conversion which converts an optical
signal into an electrical signal. The LIM reduces a power
difference generated between frames. The power difference is caused
by, for example, a difference in loss owing to transmission paths
different in length or in output power of light sources. The CDR
reduces a phase difference generated between frames. The phase
difference is caused by, for example, a difference in phase owing
to transmission paths different in length.
The variable wavelength light source 302a varies oscillation
wavelength so as to change an output destination at the AWG 30a.
The modulator 303a puts a received signal on another
wavelength.
The TWC with the above-described configuration performs OEO
(Optical-Electrical-Optical) conversion, to thereby enable power of
attenuated light to be recovered and eliminate a need of an optical
amplifier, even if data is transmitted over a long distance through
an optical signal.
FIG. 62 is a block diagram illustrating a configuration example of
the FWC 1 to FWC 8 illustrated in FIG. 60.
The FWC includes: an optical burst receiver 311a; and a fixed
wavelength light source 312a. The optical burst receiver 311a
includes: an APD, a LIM, and a CDR. In FIG. 62, a transmission path
of an optical signal is indicated by a solid line, and a
transmission path of an electrical signal is indicated by a broken
line.
The APD performs photoelectric conversion. The LIM reduces a power
difference generated between frames. The power difference is caused
by, for example, losses received which are different from one port
to another of an AWG, or differences in output power of light
sources. The CDR reduces a phase difference generated between
frames. The phase difference is caused by, for example, a
difference in phase owing to a difference in optical paths of the
different AWGs 30a.
The fixed wavelength light source 312a performs wavelength
conversion such that a wavelength of a data for THRU has a
wavelength same as that of a data for ADD, so as to output the both
data to the same port in a demultiplexing unit (not shown) at a
subsequent stage.
Next is described a case where the optical TS-SW unit is a spatial
switch of broadcast and select type.
FIG. 63 is a diagram illustrating a basic configuration of a
spatial switch of broadcast and select type.
An optical TS-SW unit 30K illustrated in FIG. 63 includes: the AWG
30b that demultiplexes a wavelength multiplexed signal (WDMi); a
plurality of N.times.1 SWs 30m; a N.times.1 SW 30n for DROP; a TWC
30d for ADD; and a coupler 30p that multiplexes optical signals
from a plurality of the N.times.1 SWs 30m. The N.times.1 SWs 30m
each include a semiconductor optical amplifier (SOA).
The AWG 30b of the optical TS-SW unit 30K demultiplexes an optical
signal as a wavelength multiplexed signal (WDMi). A coupler 30g of
the optical TS-SW unit 30K transmits the demultiplexed wavelength
components to a plurality of the N.times.1 SWs 30m. Each of the
N.times.1 SWs 30m controls transmission or interruption (through
control) of a signal using the semiconductor optical amplifier
(SOA). One of the N.times.1 SWs 30m is used as a port for DROP. The
coupler 30p: multiplexes an output from the others of the N.times.1
SWs 30m and an output from the TWC 30d for ADD; and transmits the
multiplexed output as a wavelength multiplexed signal (WDMo) to the
subsequent stage. The N.times.1 SWs 30m each include: SOAs for each
input port; a SOA of an output port; and a spatial switch. If the
number of ports is N, the number of SOAs to be controlled is
N.sup.2.
FIG. 64 is a diagram illustrating another configuration example of
the spatial switch of broadcast and select type.
An optical TS-SW unit 30L illustrated in FIG. 64 is similar to the
optical TS-SW unit 30K illustrated in FIG. 63 except that: the AWG
30b at the prior stage is not included; and the N.times.1 SWs 30m
using the SOAs are replaced by a wavelength variable filter 30q, so
as to switch between transmission and interruption of an arbitrary
wavelength. The wavelength variable filter 30q performs controls
transmission or interruption (through control) of a signal with
respect to an arbitrary wavelength using a wavelength filter. This
configuration does not require the AWG 30b at the prior stage,
which makes it possible to reduce the number of devices providing
control for switches from N.sup.2 units to N units, compared to the
configuration illustrated in FIG. 63.
Sixth Embodiment
Next is described a sixth embodiment with reference to related
drawings.
In an optical network according to the sixth embodiment, an optical
network by wavelength division multiplexing (WDM) also uses a
processing by time division multiplexing (TDM), by adding a concept
of a time slot (TS) in a prescribed time period. In the network, TS
allocation and wavelength allocation is dynamically changed
according to an incoming traffic volume. This realizes a dynamic
bandwidth allocation according to point-to-point traffic volume,
and thus improves traffic accommodation efficiency of the entire
system. When wavelength division multiplexing alone is used,
because different wavelengths are used between different points to
points, a problem of data collision occurred in a fiber network can
be ignored. In the optical network according to this embodiment,
however, because the TS is also used, it is necessary to accurately
control transmission and reception timing of each node, also taking
a propagation delay into account. Thus, in the optical network
according to this embodiment, a master node and an optical switch
node which corresponds to an OADM node in a conventional optical
network are provided, and the master node dynamically changes TS
allocation and wavelength allocation at each optical switch
node.
FIG. 65A and FIG. 65B are diagrams each illustrating an outline of
operations in the optical network according to this embodiment.
Herein, as illustrated in FIG. 65A, an optical switch node 121 is
installed at each of points A to D, and data is transmitted between
the points via a ring-shaped optical network by means of optical
communications. The master node 120 is provided that instructs the
optical switch node 121 to perform TS allocation and change over an
optical switch. Though the master node 120 is herein illustrated
separately from the optical switch node 121, any of the optical
switch nodes 121 may be configured to serve as the master node 120.
That is, the master node 120 may be provided in any of the optical
switch nodes 121. The optical switch node 121 performs data
transmission and switching in accordance with allocated TS
information, as indicated by an arrow Y10 from the master node 120.
This makes it possible to transmit a plurality of pieces of data
having the same destinations using single wavelength, without
generating data collision. In the illustrated example, a plurality
of pieces of data transmitted from the points A to C, to the point
D are all transmitted using a single wavelength .lamda.1. In order
to prevent data collision, as illustrated in FIG. 65B, <1>,
<2>, and <3> of the time slots TS are allocated to the
points A, B, and C, respectively. Further, in this configuration,
the WDM can be realized by a change in wavelengths used in
<1>, <2>, and <3> of the time slots TS. For
example, for different destinations, different wavelengths are
used, and, for the same destination, time slots are allocated for
each transmission source node.
FIG. 66A is a diagram illustrating a configuration of another
optical network system according to this embodiment. A ring optical
network is provided, on which are installed: the master node 120;
and a plurality of the optical switch nodes 121. The optical
network includes: a unidirectional transmission data line 122 that
is used for transmitting a data; and control lines 123, 124 each of
which is used for transmitting a controlled data. The control line
123 transmits control information on a network clockwise in the
figure, and the control line 124 transmits control information
counterclockwise in the figure.
The optical network system is a WDM/TDM ring network with N
wavelength multiplexing which uses both wavelength multiplexing and
time multiplexing making use of a time slot (TS), to thereby
perform ADD/DROP of data. In the network system, bandwidth
allocation is dynamically performed according to a traffic volume
from an external network. The bandwidth allocation can be realized
by changing a wavelength and a TS allocated amount defined in the
optical network system. At an entrance of the optical network
system, a data from the external network is converted into a data
in a time slot, in accordance with the TS allocated amount. On the
other hand, inside the optical network system, switching is
performed bufferless/headerless by WDM/TDM where light is as it
is.
The master node 120 has functions as follows:
(a) periodically collect a traffic volume coming from each of the
optical switch nodes 121; and determines a TS allocated amount to
be allocated to each of the switch nodes, by making the TS
allocated amount correspond to the traffic volume;
(b) specify a timing for an operation start according to the
allocated TS, taking into account a transmission delay time between
buffers of different optical switch nodes 121; and
(c) carry out re-allocation of a time slot according to the traffic
volumes collected from each of the optical switch nodes at
intervals of a prescribed time period (T). As described above, the
master node 120 may be provided in the optical switch node.
Each of the optical switch nodes 121 includes a WDM/TDM switch. The
optical switch node disposed at an edge of the optical network
includes a buffer unit that performs TS conversion, in addition to
the WDM/TDM switch. The optical switch node 121 has functions as
follows:
(a) accumulate an input signal from an external network in the
buffer unit; and notifies the master node 120 of a data amount for
each destination;
(b) change a route for data transmission (ADD) from the buffer unit
thereof and for the WDM/TDM switch, according to a TS table set by
the master node 121; and
(c) perform an operation of transmission/switching according to a
TS table in which information on an operation in a prescribed
period (period t), until the master node 121 updates the TS table.
The optical switch node 121 as described above includes an optical
TS-SW unit that realizes ADD/DROP and WDM/TDM switching, which will
be detailed hereinafter.
In transmitting information between the master node 120 and the
optical switch node 121, a wavelength for control which is
different from that for data is used. Or, a fiber which is
different from that for data (for example, control lines 123, 124
as illustrated) is used. This is to ensure reachability of the TS
table for operating an active optical TS-SW unit (WDM/TDM switch)
to each of the optical switch nodes 121. The master node 120
performs TS allocation to a control signal and a data signal
transmitted from the optical switch node 121, so as not to occur
packet collision on the ring. Note that there are two types of
signal lines connected to the optical TS-SW unit, namely, a control
signal which transmits a control packet and a control signal which
transmits a data packet. The buffer unit of the optical switch node
121 may not be necessarily provided in the same unit and may be
thus disposed at a geographically distant location. In this case,
the system is preferably configured to further include a mechanism
for measuring a distance such as a delay measurement between the
buffer unit and the switch control unit. Further, a control signal
line and a data line between the optical switch nodes 121 may share
one fiber by means of wavelength multiplexing.
FIG. 66B is a diagram illustrating an example of TS allocation in
which the optical switch nodes 121 indicated by <1> to
<3> in FIG. 66A each transmit data to the optical switch
nodes 121 indicated by A and B (B is also the master node 120) in
FIG. 66B. The optical switch nodes 121 indicated by <1> to
<3> each transmit the data at the allocated time slot, and
repeat the transmission using the same time slot until the time
slot is reallocated.
In the optical network system according to this embodiment, it is
necessary to accurately control transmission and reception timing
at the optical switch node. Two types of configurations are thus
assumed, namely, a trigger type and a time synchronization type.
The configuration of the master node 120 and the optical switch
node 121 varies depending on whether the trigger type or the time
synchronization type is used.
The optical switch node 121 of trigger type performs slot
transmission and switching at an exact moment when TS information
(a trigger) arrives thereto from the master node 120, on an
assumption that a control packet and a data packet pass through the
same route, that is, have the same propagation delay time. This can
prevent slot collision between the optical switch nodes from
occurring, without taking propagation delay into account.
The optical switch node 121 of time synchronization type measures
propagation delay times between the buffers as well as between the
optical switch nodes, and performs time synchronization control,
taking the propagation delay into account, even when a control
packet and a data packet do not pass through the same route. This
can prevent slot collision between the optical switch nodes from
occurring.
FIG. 67A illustrates a configuration of the master node 120 of
trigger type. FIG. 67B illustrates a configuration of the optical
switch node 121 of trigger type. In the figures, a solid-line arrow
indicates a path of a data signal, and a broken-line arrow
indicates a path of a control signal.
The master node 120 of trigger type includes: a demultiplexing unit
131 that wavelength demultiplexes an optical signal entering from a
transmission path; a multiplexing unit 132 that wavelength
multiplexes a signal outputted to a transmission path; a control
signal reception unit 133 that receives a control signal
demultiplexed by the demultiplexer (demultiplexing unit) 131; a
traffic information collection unit 134 that organizes traffic
information transmitted from each of the optical switch nodes; a
topology management unit 135 that manages information on connection
of an optical TS-SW unit of the optical switch node; a TS
allocation unit 136 that performs TS allocation to the optical
switch node 121, based on the traffic information organized by the
traffic information collection unit 134 and the topology
information obtained by the topology management unit 135; a TS
start delivery unit 137 that generates a trigger pulse at regular
intervals; and a TS information delivery unit 138 that delivers the
TS information with the trigger pulse to each of the optical switch
nodes.
The optical switch node 121 of trigger type includes: a
demultiplexing unit 141 that wavelength demultiplexes an optical
signal entering from a transmission path; a multiplexing unit 142
that wavelength multiplexes a signal to be outputted to
transmission path; a control signal reception unit 143 that
receives a control signal demultiplexed by the demultiplexer
(demultiplexing unit) 141; an optical TS-SW unit 144 that is
disposed between the demultiplexing unit 141 and the multiplexing
unit 142, and realizes ADD/DROP and WDM/TDM switching; a TS
synchronization unit 145 that is connected to the control signal
reception unit 143 and realizes time slot synchronization; a TS
transmit-receive unit 146 that has a buffer for accumulating a data
inputted from an external unit, transmits the data from the buffer
to the optical TS-SW unit 144, receives a data from the optical
TS-SW unit 144, and transmits the data to the external unit; and a
traffic information transmission unit 147 that transmits an amount
of data accumulated in the buffer of the TS transmit-receive unit
146, to the traffic information collection unit 134 of the master
node 120. Herein, the TS synchronization unit 145: detects a
trigger for synchronizing timing of time slots of the optical
switch node, from the signal received by the control signal
reception unit 133; counts an elapsed time from receipt of trigger
information notification; and instructs the TS transmit-receive
unit 146 and the optical TS-SW unit 144 to transmit the data at a
time slot allocated to the node itself, according to the time slot
information notified with the trigger information. In response to
the switching instruction from the TS synchronization unit 145, the
optical TS-SW unit 144 switches a route, and the TS
transmit-receive unit 146 transmits the data from the buffer to the
optical TS-SW unit 144.
FIG. 68A illustrates a configuration of the master node 120 of time
synchronization type. FIG. 68B illustrates a configuration of the
optical switch node 121 of time synchronization type. In the
figures, a solid-line arrow indicates a path of a data signal, and
a broken-line arrow indicates a path of a control signal.
The master node 120 of time synchronization type has a
configuration similar to that of trigger type illustrated in FIG.
67A except that the former further includes a time delivery unit 39
that delivers a local time of the node itself to each of the
optical switch node. In the master node 120 of time synchronization
type, instead of generating a trigger pulse by the TS start
delivery unit 137, the optical switch node specifies a time of an
operation start based on the TS information, and the TS information
delivery unit 138 delivers the TS information to each of the
optical switch nodes.
The optical switch node 121 of time synchronization type has a
configuration similar to that of trigger type illustrated in FIG.
67B, except that the former further includes a TS information
management unit 148 that holds received time slot information. The
TS synchronization unit 145: detects a control signal for
synchronizing timing of time slots of nodes; notifies a time
counter (not shown) of a time stamp value in the signal; and
instructs the TS transmit-receive unit 146 and the optical TS-SW
unit 144 to transmit appropriate data at a time slot allocated to
the node itself, according to a time slot start time (which may
also be referred to as a TS start time hereinafter) in the
signal.
If you compare the trigger type with the time synchronization type,
in the trigger type, the master node 120 simultaneously delivers
time slot information and a trigger indicating a time slot start to
each of the optical switch nodes 121. This eliminates a need for
providing the TS information management unit 148 in each of the
optical switch nodes 121. Note that, by increasing the number of
fibers of a transmission path, the demultiplexing units 131, 141
and the multiplexing unit 132, 142 can be omitted from each of the
configuration illustrated in FIG. 67A and FIG. 67B, and FIG. 68A
and FIG. 68B.
In the optical network system, the master node 120 collects traffic
information from each of the optical switch nodes 121. In this
case, it is necessary to avoid collision of traffic information
from a plurality of the optical switch node 121 with respect to a
fiber or a wavelength for control. Thus, the master node 121 also
performs time slot allocation for transmitting a control signal. In
this embodiment, each of the optical switch nodes 121 is thus
configured to start time slot counting for a control signal from a
moment when a control signal transmission TS allocation signal is
received. Slot numbers are incremented by 1 for each time slot,
with the slot number of a time slot at the start as 1. When the
incremented slot number matches a time slot number described in the
control signal transmission TS allocation signal, the optical
switch node can transmit traffic information (for each TS
transmit-receive unit) to the master node 120. Note that the time
slot is circular, and the optical switch node 121 can transmit a
control signal at regular intervals.
FIG. 69 is a diagram illustrating a procedure of transmitting
traffic information from the optical switch node 121 to the master
node 120 under the control as described above.
Next is described the procedure. In step 211, the master node 120
performs allocation of a time slot for control to each of the
optical switch nodes 121, using a control signal. In step 212, the
optical switch node 121 receives a data packet transmitted from an
external communication device 190 and measures a traffic volume. In
step 213, the optical switch node 121 transmits the traffic volume
as traffic information to the master node 120.
In step 214, the master node 120: acquires a traffic volume from
the traffic information; and calculates an allocation amount (time
slot length) of a time slot according to the traffic volume. In
step 215, the master node 120 notifies the optical switch node 121
of the calculated time slot length. In step 216, the optical switch
node 121: sets a time slot having the notified time slot length;
and transmits data accordingly.
Next is described an example of traffic information notified from
the optical switch node 121 to the master node 120.
One example of a traffic information notification is a notification
which notifies a data size accumulated in a buffer of the TS
transmit-receive unit 146 and a predicted time of how long it will
take to generate a buffer overflow. The predicted time of how long
it will take to generate a buffer overflow used herein means an
estimation of how many seconds later a buffer of the TS
transmit-receive unit 146 generates a buffer overflow. By notifying
the master node 120 of the predicted time, a larger TS can be
allocated preferentially to a virtual queue in the transmit-receive
unit 146 in which a buffer overflow may be possibly generated, thus
allowing the buffer overflow to be prevented.
FIG. 70 is a diagram for explaining how to predict a buffer
overflow. It is assumed herein that the TS transmit-receive unit
146 has a plurality of virtual queues 1 to N set therein. How many
seconds later the buffer overflows is predicted from a degree of
reduction of a remaining memory capacity in the virtual queue. Let
.DELTA.T be a time interval between time t and time t+1, during
which the remaining memory capacity of the virtual queue is assumed
to reduce by .DELTA.data. Then, [(Remaining memory capacity at time
t+1)/.DELTA.data].times..DELTA.T is a predicted time until a buffer
overflow is generated.
Alternatively, such information may be notified the master node 120
of: (a) a total current accumulated data amount; and (b) a maximum
TS amount that is not larger than a set threshold, as the traffic
information. FIG. 71 is a diagram illustrating a relation of the
threshold, the total current accumulated data amount (indicated by
[a]) represented by an upstream data frame, and the maximum TS
amount that is not larger than the threshold (indicated by
[b]).
Next is described a specific example of TS start delivery and TS
synchronization in the configuration of trigger type.
FIG. 72 is a diagram illustrating various assumed examples when the
TS start delivery and the TS synchronization is performed using a
trigger. It is assumed herein that a trigger and a data are
transmitted through the same path by means of, for example,
wavelength multiplexing.
FIG. 73 is a diagram for explaining a relation between a time slot
and a trigger. As illustrated in No. 1011 of FIG. 72, an example in
which a trigger is outputted for each time slot is illustrated in
.asterisk-pseud.1 of FIG. 73. As illustrated in No. 1012 or No.
1013, an example in which a trigger is outputted for each TS period
is illustrated in .asterisk-pseud.2 of FIG. 73. As illustrated in
No. 1014 or No. 1015 of FIG. 72, in which a trigger is outputted
for each n times the TS period is illustrated in .asterisk-pseud.3
of FIG. 73.
FIG. 74 is a diagram illustrating an operation example in which, in
a case illustrated in No. 1011 of FIG. 72 (in .asterisk-pseud.1 of
FIG. 73), a data is each transmitted from node A to node B, from
node A to node C, and from node B to node C. As illustrated in [1],
the master node 120 sets TS information to each of the optical
switch nodes. A TS number of a time slot to be inserted (ADD) in
one wavelength is determined so as not to duplicate among the
nodes. The TS length is set at one over the integers of a length of
a ring. The length of a ring used herein means a propagation delay
when a signal circulates through a ring. Then, as illustrated in
[2], the master node 120 transmits a trigger at intervals of the TS
length. The trigger makes one round of the ring because a ring
network is assumed herein. The trigger after making one round of
the ring terminates at the master node 120. As described above, a
trigger transmitted is sequentially received by each of the nodes.
As illustrated in [3], upon receipt of a trigger, node A performs
an operation in line 1 of the TS information after an offset time
(herein, 5 counts) (that is, inserts (performs an ADD of) a data of
node B as a destination at a time slot TS0). Similarly, upon
receipt of the next trigger, node A performs an operation in line 2
of the TS information. Upon receipt of a further next trigger, node
A performs an operation in line 3 of the TS information (that is,
performs an ADD of a data of node C as a destination to a time slot
TS2). The data is also received by node B because the trigger
propagates on the ring. As illustrated in [4], however, upon
receipt of the trigger, node B performs an operation in line 1 of
the TS information after the offset time (5 counts) (that is,
branches (performs a DROP of the data at a time slot TS0).
Similarly, upon receipt of a still further next trigger, node A
performs an operation of the TS information (performs an Add of the
data of node C as a destination to TS1).
As described above, the allocated TS is subjected to such
processings as ADD and DROP.
FIG. 75 is a diagram illustrating an operation example in which, in
a case illustrated in No. 1012 and No. 1013 of FIG. 72 (in
.asterisk-pseud.2 of FIG. 73), a data is each transmitted from node
A to node B, from node A to node C, and from node B to node C. As
illustrated in [1], the master node 120 sets TS information to each
of the optical switch nodes 121. A TS number of a time slot to be
inserted (ADD) in one wavelength is determined so as not to
duplicate among the nodes. The TS length is set such that the TS
period (TS length.times.m) becomes one over the integers of the
length of the ring. Then, as illustrated in [2], the master node
120 transmits a trigger at intervals of the TS period. The trigger
after making one round of the ring terminates at the master node
120. As illustrated in [3], upon receipt of the transmitted
trigger, node A sequentially performs operations in lines 1 through
m of the TS information after an offset time (herein, 5 counts)
from the receipt of the trigger. That is, node A performs ADD of
the data of node B as a destination to the time slot TS0 after the
offset time, and also performs an Add of the data of node C as a
destination to the time slot TS2 after 45 counts (offset time+TS
number.times.TS length=5+2.times.20). Similarly, as illustrated in
[4], upon receipt of the trigger, node B sequentially performs
operations in lines 1 through m of the TS information after an
offset time (herein, 5 counts) from the receipt of the trigger.
That is, node B performs a DROP of the data at TS0 after the offset
time, and performs an ADD of the data of the destination node C to
TS1 after 25 counts (offset time+TS number.times.TS
length=5+1.times.20).
FIG. 76 is a diagram illustrating an operation example in which, in
cases illustrated in No. 1014 and No. 1015 of FIG. 72 (in
.asterisk-pseud.3 of FIG. 73), a data is each transmitted from node
A to node B, from node A to node C, and from node B to node C. As
illustrated in [1], the master node 120 sets TS information to each
of the optical switch nodes 121. A TS number of a time slot to be
inserted (ADD) in one wavelength is determined so as not to
duplicate among the nodes. The TS length is set such that the TS
period (TS length.times.m) becomes one over the integers of the
length of the ring. Then, as illustrated in [2], the master node
120 transmits a trigger at intervals of the TS period.times.n. The
trigger after making one round of the ring terminates at the master
node 120. As illustrated in [3], upon receipt of the trigger, node
A sequentially performs operations in lines 1 through m of the TS
information after an offset time (herein, 5 counts) from the
receipt of the trigger. After performing the operation in line m,
node A repeats the operations in lines 1 through m until node A
receives the next trigger. As illustrated in [4], upon receipt of
the trigger, node B sequentially performs operations in lines 1
through m of TS information after an offset time (herein, 5
counts), and repeats the operations until node B receives the next
trigger. Upon receipt of the next trigger, similarly, node B the
operations in lines one through m of the TS information.
Next is described a relation among a ring length, a TS length, and
a TS period.
When a master node and a plurality of optical switch nodes are
arranged in a ring network, it is sometimes necessary to transmit
or receive a data across the master node in the network. FIG. 77A
is a diagram illustrating a network configuration in the case. In
the figure, when a data is transmitted from node C to node A, it is
necessary to transmit the data across the master node 120. Thus, as
illustrated in FIG. 77B, the TS length or the TS period may be set
at one over the integers of the ring length so as to receive the
data across the master node 120 (if a trigger output interval is
the TS length, the TS length is set at one over the integers of the
ring length, and, if the trigger output interval is a TS period or
a TS period.times.N, the TS period is set at one over the integers
of the ring length). This makes it possible for node A to receive a
data transmitted from node C using a trigger newly-transmitted from
the master node 120.
In some cases, transmission and reception timing of time slots of
the nodes is deviated due to fluctuations of a clock or the like.
For example, a trigger output interval of the master node 120 may
fluctuate. When a time slot is periodically transmitted as
illustrated in No. 1014 and No. 1015 of FIG. 72, the transmission
and reception timing of the time slot may be deviated. FIG. 78 is a
diagram for explaining deviation of timing of a time slot. If
clocks are matched, timing of time slots received by the nodes 120
and A to C coincides. However, when, for example, a clock is fast
in node A or is slow in node B owing to clock fluctuations, there
is a possibility that timing of the time slots TS1 and TS2 is
deviated, to thereby generate an overlap of the time slots between
nodes A to C. Hence, in order to prevent data collision even when
such a clock fluctuation is generated, as illustrated in FIG. 79,
guard times are set before and after a data in a clock slot, taking
into account the overlap of the time slots owing to the clock
fluctuation.
Next is described a relation between a ring topology in a trigger
type configuration and a configuration of an optical switch
node.
In the ring network, data may be transmitted in whichever
direction, unidirectionally (either one of clockwise and
counterclockwise) or bidirectionally (both clockwise and
counterclockwise). Because a trigger in the network is transmitted
in a route same as that of a data, the trigger can be transmitted
in whichever direction, unidirectionally or bidirectionally. FIG.
80A is a diagram illustrating a configuration of the optical switch
node 121A on a unidirectional ring. In FIG. 80A, illustration of
traffic information transmission unit 147 is omitted, which makes
the optical switch node 121A equivalent to that illustrated in FIG.
67B or FIG. 68B. Meanwhile, FIG. 80B illustrates a diagram of a
configuration of the optical switch node 121B suited for a
bidirectional ring. If the physical topology is bidirectional, the
optical switch node 121B is equipped with a pair of control signal
reception units 143a, 143b and a pair of TS information management
units 148a, 148b, each for clockwise and counterclockwise, are
provided. The master node 120 transmits a trigger both clockwise
and counterclockwise. Based on appropriate TS information in the TS
information management unit 148a, 148b corresponding to directions
in which the trigger is transmitted or received, each of the
optical switch nodes 121A, 121B performs data transmission and
receipt and switching in a direction same as that of the trigger
transmission and receipt.
Next is described in detail a configuration of time synchronization
type. The time synchronization type is characterized in that a TS
start is specified by a time. In synchronization by the
above-described trigger type, it is necessary to transmit a trigger
and a data in a same route. In the TS synchronization by the time,
a TS start time can be set previously. Also, it is not necessary to
deliver a TS start time on a route same as that of a data. How to
set a time of each of the nodes in the case of the time
synchronization type includes: (a) setting a time in which a delay
time corresponding to a data transmission path is added to a time
at the master node 120, to each of the nodes; and (b) setting a
common time to all of the master node 120 and the optical switch
nodes 121. (a) setting a time to which a delay time is added (a
time with delay difference) is characterized in that all of the
nodes can have the same value of the TS start time in common. (b)
setting of a common time is characterized in that the time can be
set making use of the GPS (Global Positioning System) or the
like.
Next is described the time setting using the time with delay
difference. When a TS start delivery and a TS synchronization are
set using the time with delay difference, a time to which a time
difference corresponding to a delay time between nodes is set to
each of the nodes. In this case, how to set the TS start delivery
and the TS synchronization can be achieved in several ways as
illustrated in FIG. 81.
How to deliver information as a control signal for the setting by
the master node 120 includes: a TS start time, a time stamp, and TS
information are combined together and then transmitted, as
indicated by reference character SS20 in FIG. 82; and those
described above are separately transmitted as indicated by
reference characters SS21 to SS23 in FIG. 82. In the latter case,
because the time stamp is transmitted individually, deviation of a
counter value can be corrected.
With respect to a direction of transmitting a control signal with a
time stamp from the master node 120, a unidirectional setting and a
bidirectional setting can be assumed whether or not a ring topology
is a unidirectional topology or a bidirectional topology. FIG. 83A
is a diagram illustrating an example in which the master node 120
transmits a control signal counterclockwise, as indicated by arrow
Y1. If the master node 120 transmits a control signal with a time
stamp at a local time t, a delay is accumulated while the control
signal is transmitted through a node 121a, a node 121b, and a node
121c. Upon receipt of the control signal with the time stamp, each
of the nodes 121a to 121c sets the time stamp of the control signal
to a time counter thereof. As a result, each of the set local times
is set at a time shifted by a delay time. FIG. 83B is a diagram
illustrating an example in which the master node 120 transmits a
control signal clockwise, as indicated by arrow Y2.
In the bidirectional setting, the master node 120 transmits a
control signal with a time stamp either clockwise or
counterclockwise. Because a clockwise delay is naturally different
from a counterclockwise delay at a given node, each of the nodes
has a clockwise and a counterclockwise time counters and manages
respective local times thereof.
FIG. 84A is a diagram illustrating a configuration of an optical
network system. FIG. 84B is a diagram illustrating a time setting
time chart of time synchronization using a time with delay
difference. In optical network system according to this embodiment,
the master node 120 controls each of the optical switch nodes
(which may also be simply referred to as switch nodes or nodes)
121a, 121b by specifying an optical switch switching time and a
packet transmission time. This means that the master node 120 needs
to set a time of each of the switch nodes 121a, 121b. As indicated
by [1] in the figure, the master node 120 transmits a time setting
packet with a time stamp given thereto to each of the optical
switch nodes 121a, 121b. As illustrated in [2], each of the optical
switch nodes 121a, 121b upon receipt of the time setting packet,
sets a value described in the time stamp as a current time of its
own. At this time, a relation as follows holds: Each of times set
to the optical switch nodes 121a, 121b=Time at master node-Each of
respective unidirectional propagation delay times. Because the
master node 120 previously has the unidirectional propagation delay
time, the master node 120 can also obtain the time set to each of
the optical switch nodes 121a, 121b.
Meanwhile, in order to previously have the unidirectional
propagation delay time to each of the nodes 121a, 121b, the master
node 120 needs to measure an actual delay thereof. A propagation
delay time can be measured in such a manner that a time stamp given
by the master node 120 is transmitted and received between the
master node 120 and the optical switch nodes 121a, 121b while the
time stamp is made to go and return in the same route.
FIG. 85A and FIG. 85B are diagrams each for explaining such a delay
time measurement. As illustrated in the figures [1], the master
node 120 transmits a time setting packet with a time stamp given
thereto. As respectively illustrated in [2] and [3], upon receipt
of the time setting packet, the optical switch nodes 121a, 121b
return a delay measurement packet containing the time stamp given
by the master node 120, as a acknowledgment packet to the master
node 120. As illustrated in [4], the master node 120 calculates a
unidirectional propagation delay time based on a difference from an
arrival time of the acknowledgment packet to a time of the first
time stamp. In practice, because a processing delay at the optical
switch is present as illustrated in the figures, a time required
for the processing should be included in the calculation.
Also in the case of time synchronization using the time with delay
difference, similarly to the case of trigger type, a configuration
of the optical switch node varies according to whether the physical
topology is of unidirectional ring or bidirectional ring. FIG. 86A
is a diagram illustrating an optical switch node 121A suited for
the unidirectional ring. The optical switch node 121A is
substantially similar to the optical switch node 121 of FIG. 68B,
except that: illustration of the traffic information transmission
unit 147 is omitted; and the time counter 149 and the internal
clock 150 are illustrated so as to make clear the time
synchronization performed by the TS synchronization unit 145.
On the other hand, in the case in which the physical topology is
bidirectional, the optical switch node 121B includes a pair of:
control signal reception units; TS information management units;
and time counters, each for clockwise use and for counterclockwise
use. FIG. 86B illustrates, as those for clockwise use, a control
signal reception unit 143b, a TS information management unit 148b,
and a time counter 149b. The master node 120 transmits a control
signal both clockwise and counterclockwise of a ring. Each of the
optical switch nodes 121A, 121B performs an appropriate operation
based on TS information of the TS information management unit and
the time counter corresponding to transmission and receipt
directions of the control signal. For example, in response to a
clockwise control signal, the
TS information management unit 48b for clockwise use is
operated.
On the other hand, in the case of the time synchronization using
time with delay difference, each of the nodes has a local time set
with a time difference corresponding to a delay from a time of the
master node. Thus, if a data is transmitted in a direction same as
that in which a time stamp has been transmitted, a relation as
follows holds: "Reception time of local time of receiving
node"="Transmission time of local time of transmitting node". For
example, in a case illustrated in FIG. 87A and FIG. 87B, when the
master node 120 transmits a data at a local time=t1, each of the
nodes 121a to 121c receives the data at a local time=t1 of its own.
However, in a case in which each of the nodes 121a to 121c
transmits a data to the master node 120 or any of the nodes 121a to
121c transmit or receive a data therebetween, jumping over the
master node 120, a relation as follows holds: "Reception time of
local time of receiving node"="Transmission time of local time of
transmitting node"+"Time required for making one round of a ring
(a+b+c+d)". For example, if the node 121a transmits a data at a
local time=t2 of its own, the master node 120 receives the data at
a local time of its own=t2+a+b+c+d. In order to branch (DROP) the
data at the master node 120, it is necessary to set a DROP
switching time at the master node 120, at "TS start time+Ring
one-round time". Similarly, in a case of transmitting or receiving
a data, jumping over the master node 120, such as from the node
121c to the node 121a, it is necessary to set the DROP switching
time at "TS start time+Ring one-round time" or perform a TS setting
in reverse so as not to jump over the master node 120.
How to calculate or set a ring one-round time includes, for
example: measuring a delay time using a measuring instrument such
as an OTDR (Optical Time Domain Reflectometer) and setting a result
of the measurement in the TS information management unit manually
or the like; and calculation based on a control signal which makes
one round in the ring. In the case of calculating based on the
control signal subjected to one round of the ring, for example, the
master node generates and transmits a control signal with a time
stamp given thereto. A delay measurement function unit (not shown)
of the master node receives the control signal after making one
round of the ring, and calculates a ring one-round time by
subtracting a time stamp value from a reception time.
FIG. 88 is a diagram illustrating an operation example in which a
local time and a TS start time are delivered in a configuration of
time synchronization type using a time with delay difference in a
case of No. 2013 of FIG. 81. It is assumed herein that all TSs are
already set. As illustrated in [1], the master node 120 time slot
information to node A. As illustrated in [2], the master node 120
transmits a control signal containing a TS start time and a time
stamp value for each TS period. As illustrated in [3], upon receipt
of the control signal, node A sets a time counter of its own as a
time stamp value of the control signal. As illustrated in [4], node
A sequentially starts operations at a time slot TS0, when the time
counter reaches the TS start time. That is, node A performs an
operation of the TS information when "TS start time+TS
number.times.TS length" has arrived.
In a case of the illustrated node A, the node A: performs an ADD at
the time slot TS0 of time counters 100 to 120; and performs an ADD
to a time slot TS2 at time counters 140 to 160. Node A repeats the
operation until the next TS start time is transmitted. Then, as
illustrated in [5], upon receipt of another control signal, node B
sets a time counter of its own as a time stamp value of the control
signal. As illustrated in [6], node B sequentially starts
operations at a time slot TS0, when the time counter reaches the TS
start time. In a case of the illustrated node B, the node B:
performs a DROP of TS0 at the time counters 100 ((time counter=TS
start time+TS number.times.TS length) to 120; and performs an ADD
to S2 at time counters 120 to 140. Node B repeats the operation
according to the TS information until the next TS start time is
transmitted.
Next is described the time synchronization using a common time.
In this case of the common time, each of the nodes independently
sets a time thereof based on the common time. This makes it
unnecessary to deliver a signal for setting a local time of each of
the nodes. The common time used herein is information on time which
any of the nodes can obtain independently of the others. The common
time is thus a single time system and does not depend on a
propagation delay at each of the nodes. The common time as
described above includes: a high-accuracy internal clock installed
at each of the nodes (for example, an atomic time standard such as
a cesium oscillator and a rubidium oscillator, and a crystal
oscillator); and an external clock equally shared by each of the
nodes (for example, a GPS clock and a JJY clock (Japan standard
atomic radio clock)). When the internal clock is used for each of
the nodes, a time thereof is set at an identical and the most
accurate time with high accuracy. The TS synchronization using the
common time can be achieved in several ways as illustrated in FIG.
89.
Even if all local times of the nodes including the master node and
the optical switch nodes are matched with accuracy by using the
common time such as the GPS, it is still necessary to prevent data
collision taking a delay between the nodes into account in
allocating a time slot. A delay therefore needs to be measured even
in the case of using the common time.
FIG. 90A is a diagram illustrating a configuration of an optical
network system. FIG. 90B is a diagram illustrating a procedure of
delivering a common time to each of the nodes using the GPS, and
measuring a delay.
The master node 120 and the optical switch nodes 121a, 121b are
each connected to a GPS receiver, to thereby set an accurate time
obtained from the GPS, as a local time of each of the nodes 120,
121a, 121b. As illustrated in [1], the master node 120 transmits a
delay measurement packet to which a time (T1) inside the master
node itself is given as a time stamp. As illustrated in [2], upon
receipt of the delay measurement packet, each of the nodes 121a,
121b calculates a propagation delay time from a value of the time
stamp in the received packet (at T1) and a current time at the node
itself, that is, "Propagation delay time=Current time-Time stamp
value. As illustrated in [3], each of the nodes 121a, 121b notifies
the master node 120 of the measured propagation delay time.
Note that the time synchronization using the common time does not
necessarily require doubly-provided control signal lines (clockwise
and counterclockwise control lines), and a singly-provided or a
unidirectional control line can also be used. Each of the nodes can
transmit the measured propagation delay time without collision, by
performing a TS allocation in a direction same as that of the delay
measurement packet.
Next is described a TS start time in a case in which the time
synchronization is performed using a common time. In the time
synchronization using the common time, local times of each of the
nodes are accurately matched. It is thus necessary to take a delay
between the nodes into account so as to determine a start time of a
time slot such that no data collision occurs. That is, it is
necessary for each of the nodes to update the TS start time by
adding a delay time from that of the master node to a TS start time
"t" which is transmitted by the master node. FIG. 91A and FIG. 91B
are diagrams each for explaining how to determine such a TS start
time.
In the explanation, as illustrated in FIG. 91A, designated at [1]
is the ring-connected master node 120; at [2], the node 121a; and
at [3], the node 121b, which may be collectively referred to as
each of the nodes [1] to [3]. Also in FIG. 91B, the nodes are
indicated by respective numeric characters [1] to [3].
In a counterclockwise direction of the ring illustrated in FIG.
91A, a TS start time of the master node [1] corresponds to a time
t1 in FIG. 91B. In the counterclockwise direction, let "a" be a
delay time between the master node [1] and the node [2] in
transmitting a signal. The TS start time at the node [2] in the
counterclockwise direction is "t1+a=t2". Similarly, let "a+b" be a
delay time between the master node [1] and the node [3]. The TS
start time at the node [3] in the counterclockwise direction is
"t1+a+b=t3".
In a clockwise direction, let "c" be a delay time between the
master node [1] and the node [3]. The TS start time at the node [3]
in the clockwise direction is "t1+c=t2a". Similarly, let "c+b" be a
delay time between the master node [1] and the node [2]. The TS
start time at the node [2] in the clockwise direction is
"t1+c+b=t4".
Next is described a processing of recognizing a topology at the
topology management unit 135 of the master node 120. FIG. 92 is a
time sequence diagram illustrating operations of recognizing a
topology in the case of a single control ring.
The master node 120 requests an ID (identification number) of a
switch thereof, an ID of an interface (TS transmit-receive unit) of
the switch, and the like from each of the optical switch nodes 121
(ID request S1), so as to recognize a connection configuration
between the optical switch nodes 121 connected to a ring network
and a terminal (external communication device) 190 connected to the
optical switch node 121. The optical switch node 121 returns an ID
response S2 to the ID request S1. The master node 120 requests, as
a managed terminal address request, an address or the like of a
terminal (external communication device) 190 connected to the
optical switch node 121, from the optical switch node 121 itself
(managed terminal address request S3). The optical switch node 121:
is notified of an updated address of the terminal 190 connected to
the optical switch node 121 (S4), each time the terminal address is
updated; and stores therein the terminal address 190m. Thus, the
optical switch node 121 notifies the master node 120 of an address
or the like of the managed terminal (external communication device)
190, as a terminal address response S5, in response to the managed
terminal address request S3. This makes it possible for the master
node 120 to recognize the switch ID of the optical switch node 121
connected to the ring network, the ID of the TS transmit-receive
unit, a port number connected to the TS transmit-receive unit of
the optical switch node 121, a port number used for establishing a
ring at the optical switch node 121, and the address of the
terminal 190 in control of the optical switch node 121.
In order to prevent collision of a data for topology management
since the single control ring is assumed herein, upon receipt of a
control signal from the master node 120, each of the optical switch
nodes 121: adds information requested by the master node 120 behind
a received packet like a string; and transmits the packet to the
optical switch node 121 at a next stage.
Next is described a configuration of transmitting a trigger and a
control signal in the optical network system according to this
embodiment. In each of the optical switch nodes, a data is required
to be transmitted to the optical switch node at the next stage via
the optical TS-SW unit or to be subjected to a DROP. A trigger (or
a control signal) is required to be transmitted to the optical
switch node at the next stage and also to be given to the control
signal reception unit of the node itself. The configuration of
transmitting the trigger or the control signal has variations, for
example, those illustrated in FIG. 93A to FIG. 93D, in each of
which the trigger or the control signal is assumed to be
transmitted at a wavelength for control .lamda.c. In explanations
with reference to FIG. 93A to FIG. 93D, it is assumed that a
trigger includes a control signal.
In FIG. 93A, a trigger is made to pass through the optical TS-SW
unit 144. The trigger branches in the optical TS-SW unit 144 and is
supplied to the control signal reception unit 143. In this case,
the optical TS-SW unit 144 is set at broadcasting.
In FIG. 93B, a trigger is also made to pass through the optical
TS-SW unit 144, and the optical TS-SW unit 144 is set at DROP and
ADD. The trigger is subjected to a DROP in the optical TS-SW unit
144 and is supplied to the control signal reception unit 143. The
control signal reception unit 143 branches the trigger. The optical
TS-SW unit 144 performs an ADD of a portion of the trigger required
to be transmitted to the next stage.
In FIG. 93C, a trigger is not made to pass through the optical
TS-SW unit 144. The trigger is branched in a state of an electrical
signal by being subjected to OE (optical/electrical)-EO
(electrical/optical) conversion with respect to the wavelength for
control .lamda.c or is branched using an optical coupler, and is
then given to the control signal reception unit 143.
In FIG. 93D, a trigger is not also made to pass through the optical
TS-SW unit 144. The trigger is branched separately from a data with
respect to the wavelength for control .lamda.c at the control
signal reception unit 143.
Next is described a connection configuration between the optical
TS-SW unit and the TS transmit-receive unit. The connection
configuration between the optical TS-SW unit and the TS
transmit-receive unit has variations, for example, those
illustrated in FIG. 94A to FIG. 94C.
In FIG. 94A, the TS transmit-receive unit 146 is configured to be 1
output 1 input. A transmitted data is stored in a separate queue in
the TS transmit-receive unit 146 for each destination. The TS
transmit-receive unit 146 is connected to the optical TS-SW unit
144 with 1 port for each of ADD and DROP.
In FIG. 94B, the TS transmit-receive unit 146 is configured to have
1 input for the entire TS transmit-receive unit 146 itself and 1
output for each queue. A transmitted data is stored in a different
queue in the TS transmit-receive unit 146 according to a
destination of the data. Connection of the TS transmit-receive unit
146 with the optical TS-SW unit 144 uses one ADD port for each
queue. One DROP port is used for the entire TS transmit-receive
unit 146. Usage of one ADD port for each queue makes it possible
for data with different destinations to be simultaneously outputted
if ring transmission directions of the data are different.
In FIG. 94C, the TS transmit-receive unit 146 is configured to
further include therein a buffer at which data is received from two
DROP ports, compared to the TS transmit-receive unit 146
illustrated in FIG. 94B. Usage of the two DROP ports makes it
possible to simultaneously receive data from both ring clockwise
and counterclockwise directions.
Next is described a configuration of the optical TS (time slot)-SW
(switch) unit 144 provided in the optical switch node 121.
As described above, the optical TS-SW unit 144: is equipped with an
input port and an output port in each of which a data line of a
ring network is accommodated; changes a connection relation between
the input port and the output port according to an instruction from
the master node 120; and also performs a processing such as
wavelength conversion where necessary. The optical TS-SW unit 144
as described above may be configured as a wavelength routing switch
using wavelength conversion or as a spatial switch of broadcast and
select type, which will be specifically described hereinafter. The
data line accommodated in the optical TS-SW unit 144 is grouped
into a multiplexed data line and a non-multiplexed data line. FIG.
95A and FIG. 95B are diagrams each illustrating an outline of the
optical TS-SW unit 144 configured as a wavelength switch. FIG. 95A
illustrates a case in which a multiplexed data line is
accommodated. FIG. 95B illustrates a case in which a
non-multiplexed data line is accommodated.
In the case of accommodating a multiplexed data line, as
illustrated in FIG. 95A, the demultiplexing unit 141 is disposed
before the optical TS-SW unit 144. A data inputted by wavelength
multiplexing is demultiplexed into, for example, N wavelengths,
which are respectively given to input ports IN 1 to IN N. A
multiplexing unit 142 is disposed at a subsequent stage of the
optical TS-SW unit 144. The multiplexing unit 142 multiplexes
optical signals from N output ports OUT 1 to OUT N of the optical
TS-SW unit 144 and transmits the multiplexed data to a next
(subsequent) node on the ring network. The optical TS-SW unit 144
also has functions of insertion of an optical signal (ADD) and
branching of an optical signal (DROP). The optical TS-SW unit 144
is equipped with a port for ADD as an input port. The optical TS-SW
unit 144 is also equipped with a port for DROP as an output
port.
In the case of accommodating a non-multiplexing data line, as
illustrated in FIG. 95B, neither demultiplexing unit nor
multiplexing unit is provided. In this case, the number of data
lines on the ring is equal to the number of end terminals (ports)
from which the number of interfaces for ADD/DROP at the optical
switch is subtracted.
FIG. 96 is a diagram illustrating a basic configuration of the
optical TS-SW unit 144 which is configured as a wavelength switch.
The optical TS-SW unit 144 is equipped with one or more input ports
and a plurality of output ports, and includes: a demultiplexer 141
that demultiplexes a multiplexed input optical signal for each
wavelength; an AGW (arrayed waveguide grating) 144i that
distributes an optical signal inputted into each of the input ports
into an appropriate output port in accordance with a wavelength of
the optical signal; TWC (variable wavelength converter: tunable
wavelength converter) 1 to TWC 8 and TWC [A]1 to TWC [A]3 each of
which perform wavelength conversion so as to select from passing
through (THRU), insertion (ADD), and branching (DROP) at the
optical switch node; a multiplexer (multiplexing unit) 142 that
multiplexes an output optical signal at each of wavelengths so as
to transmit the optical signal to a next stage; FWC (fixed
wavelength converter: fixed wavelength converter) 1 to FWC 8 each
of which performs such wavelength conversion that the optical
signals are outputted to the same port in the demultiplexing unit
at the next stage; and an optical receiver 144j that receives the
optical signals having been branched (DROP) by the AWG 144i.
In the illustrated example, the demultiplexer 141 demultiplexes the
optical signal transmitted by wavelength multiplexing from the
prior stage, into wavelengths .lamda.1 to .lamda.8. The
demultiplexed optical signals are given to respective input ports
of the AWG 144i via the TWC 1 to the TWC 8. In addition, another
optical signal to be inserted are given to respective input ports
of the AWG 144i via the TWC [A]1 to the TWC [A]3. Eight of the
output ports of the AWG 144i are for use in transmission to the
next stage. The optical signals from those output ports: are
inputted into the multiplexer 142 via the FWC 1 to the FWC 8,
respectively; are multiplexed: and are transmitted to the next
stage. The AWG 144i is further equipped with output ports used for
branching (DROP). The output ports are connected to the optical
receiver 144j. The optical receiver 144j includes: a photoelectric
device (APD) that performs photoelectric conversion; a limiting
amplifier (LIM) that absorbs power difference between optical
signals; and a clock data recovery circuit (CDR) that absorbs phase
difference between the optical signals, which are connected in
series in this order. The optical receiver 144j absorbs power
difference/phase difference between signals and receives an optical
signal. Note that in the example illustrated in FIG. 96, the
wavelength .lamda.8 is designed to be a fixed wavelength for
control. One channel of each of ADD and DROP is also designed to be
for control and is connected to a switch control unit for
controlling the optical TS-SW unit 144.
FIG. 97A is a diagram illustrating an example of a configuration of
the TWC. In the figure, an optical signal is indicated by a bold
solid line, and an electrical signal is indicated by a bold broken
line. The TWC includes, similarly to the described above: an
optical burst receiver 170 that includes an APD, a LIM, and a CDR;
a variable wavelength light source 171 that can vary oscillation
wavelength so as to change an output destination at the AWG; and a
modulator 172 that modulates light from the variable wavelength
light source 171 using an electrical signal from the optical burst
receiver 170. In the TWC, the LIM is provided so as to absorb a
difference in loss owing to transmission paths different in length
or in output power of light sources. The CDR is provided so as to
absorb a phase difference owing to transmission paths different in
length. The TWC as described above can recover power of light
attenuated due to long distance transmission, by performing
optical-electrical-optical conversion. Thus, usage of the TWC
eliminates a need of an optical amplifier.
FIG. 97B is a diagram illustrating an example of a configuration of
the FWC. In the figure, an optical signal is indicated by a bold
solid line, and an electrical signal is indicated by a bold broken
line. The FWC includes: the optical burst receiver 170 including an
APD, a LIM, and a CDR; and a fixed wavelength light source 173 that
performs wavelength conversion such that a pass-through data and an
ADD data have the same wavelength and are outputted to the same
port of the demultiplexing unit at the next stage. In the FWC, the
LIM is provided so as to absorb a difference in loss varying for
each port of the AWG or in output power of light sources. The CDR
is provided so as to absorb a phase difference due to different
transmission paths at the AWG.
The optical TS-SW unit of wavelength switch type may have various
configurations. FIG. 98 is a diagram illustrating the various
possible configurations. Herein, the possible configurations are
shown according to: how many fibers per AWG are provided; whether
or not the FWC is provided; whether a port for ADD connection is
provided at a prior stage or at a subsequent stage of the AWG; and
whether a wavelength exchange is performed between fibers or in the
fibers. If the configuration is free of the FWC, cost can be
reduced accordingly. If the wavelength exchange between fibers is
used, even if one of the optical fibers is disconnected,
communications are possible, thus improving failure resistance.
Further, if the in-fiber wavelength conversion is used, flexible
operations become possible.
Next are described some specific configuration examples of the
optical TS-SW unit of wavelength switch type.
FIG. 99 is a diagram illustrating the configuration example of the
optical TS-SW unit 144, corresponding to a case of [1] of FIG. 98
in which: a k-fold ring having k fibers is used; and N wavelengths
per ring are used. It is assumed in the figure that K=2 and N=4.
How a wavelength exchange between k fibers is performed is herein
exemplified in a case where the FWC is not provided. With respect
to kN wavelengths of .lamda.i (0.ltoreq.i.ltoreq.kN-1), a plurality
of wavelengths whose "i MOD N" take the same value are deemed as
the same wavelengths. This makes it possible to input a signal
after switching by the same wavelength unit at the wavelength
conversion unit (TWC) at a subsequent stage, without using the FWC.
More specifically, kN.times.kN circular AWGs 141a, 141b are
provided. At a subsequent stage thereof, N TWC 1 to TWC 8 and k
circular 1.times.N AWG 144i as a demultiplexing unit are provided.
At a further subsequent stage thereof, k output ports 144k, 144l
are provided.
FIG. 100 is a diagram illustrating the example corresponding to a
case of [1a] of FIG. 98 in which: the k-fold ring and N wavelengths
per ring are used; and a wavelength exchange between fibers is
performed by means of 1 ADD/1 DROP without using the FWC. It is
assumed in the figure that K=2 and N=4. With respect to kN
wavelengths .lamda.i (0.ltoreq.i.ltoreq.kN-1), a plurality of
wavelengths whose "i MOD N" take the same value are deemed as the
same wavelengths. A kN.times.kN circular AWG 144i is provided. At a
prior stage thereof: k circular 1.times.N AWGs 141c, 141d; k(N-2)
TWC 1 to TWC 4 for use in pass-through (THRU)/branching (DROP); and
one TWC [A] for use in insertion (ADD). The k circular 1.times.N
AWGs 141c, 141d each of which functions as a demultiplexing unit
that also performs wavelength conversion. The optical receiver 144j
that is an interface for branching and k (N-1).times.N multiplexing
units 142c, 142d are provided on an output side of the kN.times.kN
circular AWG 144i.
FIG. 101 is a diagram illustrating the example corresponding to
also the case of [1a] of FIG. 98 in which: the k-fold ring and N
wavelengths per ring are used; a wavelength exchange between fibers
is performed by means of 1 ADD/1 DROP without using the FWC; and a
control wavelength is also used. It is assumed in the figure that
K=2 and N=4. With respect to kN wavelengths of .lamda.i
(0.ltoreq.i.ltoreq.kN-1), a plurality of wavelengths whose "i MOD
N" take the same value are deemed as the same wavelengths. A
kN.times.kN circular AWG 144i is provided. Ata prior stage thereof:
k circular 1.times.N AWGs 141c, 141d each of which functions as a
demultiplexing unit which also performs wavelength conversion;
k(N-2) TWC 1 to TWC 4 for use in pass-through (THRU)/branching
(DROP); and one TWC [A] for use in insertion (ADD) are provided.
The optical receiver 144j that is an interface for branching, and k
(N-1).times.N multiplexing units 142c, 142d are provided on the
output side of the kN.times.kN circular AWG 144i. Further, in this
configuration, a wavelength for control is prepared for performing
switch control, and, so as to ensure reachability of the wavelength
for control, each of the demultiplexing units is connected to a
coupler 144r, at which the wavelength for control is copied.
FIG. 102 is a diagram illustrating the example corresponding to
also the case of [1b] of FIG. 98 in which: the k-fold ring and N
wavelengths per ring are used; and a wavelength exchange between
fibers is performed by means of 1 ADD/1 DROP without using the FWC.
It is assumed in the figure that K=2 and N=4. The kN.times.kN
circular AWG 144i is provided. At the prior stage thereof: k
circular 1.times.N AWGs 141c, 141d each of which functions as a
demultiplexing unit which also performs wavelength conversion; and
k(N-2) TWC 1 to TWC 4 for use in pass-through (THRU)/branching
(DROP) are provided. At the subsequent stage of the kN.times.kN
circular AWG 144i: a TWC [A] for use in insertion (ADD); an AWG
141e for branching at a subsequent stage of the TWC [A]; the
optical receiver 144j that is an interface for branching; and
k(N-1).times.N multiplexing units 142c, 142d are provided.
FIG. 103 is a diagram illustrating the example corresponding to the
case of [2] of FIG. 98 in which: the k-fold ring and N wavelengths
per ring are used; the optical TS-SW unit 144 is capable of
performing a wavelength exchange between fibers and a wavelength
exchange in fibers without using the FWC. It is assumed in the
figure that K=2 and N=4. With respect to kN wavelengths .lamda.i
(0.ltoreq.i.ltoreq.kN-1), a plurality of wavelengths whose "i MOD
N" take the same value are deemed as the same wavelengths. This
makes it possible to input a signal after switching by the same
wavelength unit at the wavelength conversion unit at a subsequent
stage, without using the FWC. More specifically, the kN.times.kN
circular AWG 144i are provided. At the prior stage thereof: the TWC
1 to TWC 8; and k circular 1.times.N AWGs 141c, 141d each of which
functions as a demultiplexing unit are provided. At the subsequent
stage thereof: k N-2 N.times.1 star coupler 144s, 144t; and k
output ports 144k, 144l are provided.
FIG. 104 is a diagram illustrating the example corresponding also
to the case of [3] of FIG. 98 in which: the k-fold ring (having N
wavelengths per ring) are used with 1 fiber per AWG; and the 1
ADD/1 DROP configuration is used without using the FWC; and a
control wavelength is used. It is assumed in the figure that K=2
and N=4. With respect to kN wavelengths of .lamda.i (i=0 to kN-1),
a plurality of wavelengths whose "i MOD N" take the same value are
deemed as the same wavelengths. k N.times.N circular AWGs (2
4.times.4 circular AWGs in the FIG. 144h, 144i are provided. Ata
prior stage of the k N.times.N circular AWGs 144h, 144i: k circular
1.times.N AWGs 141c, 141d each of which functions as a
demultiplexing unit which also performs wavelength conversion;
k(N-2) TWC 1 to TWC 4 for use in pass-through (Through)/branching
(DROP); and one TWC [A] for use in insertion (ADD) are provided.
The TWC [A] for insertion is connected to the 4.times.4 AWG 144h
which is positioned in an upper part of the figure. At the
subsequent stage of the k N.times.N circular AWGs 144h, 144i, the
optical receiver 144j that is an interface for branching; and k
N.times.N multiplexing units 142c, 142d are provided. The optical
receiver 144j is connected to the optical receiver 144j which is
positioned in a lower part of the figure. A TWC [A/D] for ADD/DROP
between the fibers is provided such that an output of the upper
4.times.4 AWG 144h is connected to an input of the 4.times.4 AWG
144i. Further, so as to ensure reachability of a wavelength for
control, each of the demultiplexing units is connected to the
coupler 144r, at which the wavelength for control is copied.
FIG. 105 is a diagram illustrating a specific example of the basic
configuration illustrated in FIG. 96. It is assumed herein that: a
double ring having 4 wavelengths per ring is used; and ADD/DROP is
performed via 1 channel. As the AWG 144i, a 9.times.9 AWG 144g is
used. Output ports of the AWG 144g except a DROP port are connected
to FWC 1 to FWC 4+FWC 1 to FWC 4, respectively. FIG. 105B is a
diagram illustrating requirements of wavelength at the TWC [A] and
TWC 1 to TWC 8 which are disposed on an input side of the AWG
144g.
FIG. 106A is a diagram illustrating the example corresponding to
the case of [0a] of FIG. 98 in which a double ring having 4
wavelengths per ring is used. At the subsequent stage of the
9.times.9 AWG 144g, the FWC 1 to FWC 4+FWC 1 to FWC 4 are provided.
ADD/DROP is performed via 1 channel. Wavelength exchange is
performed in the fibers. FIG. 106B is a diagram illustrating
requirements of wavelength at the TWC [A] and TWC 1 to TWC 8 which
are disposed on the input side of the AWG 144g.
FIG. 107A is a diagram illustrating the example corresponding to
the case of [0b] of FIG. 98 in which a double ring having 4
wavelengths per ring is used. At the subsequent stage of the
9.times.9 AWG 144g, the FWC 1 to FWC 4+FWC 1 to FWC 4 are provided.
ADD/DROP is performed via 1 channel. Wavelength exchange is
performed between the fibers as well as in the fibers. FIG. 107B is
a diagram illustrating requirements of wavelength at the TWC [A]
and TWC 1 to TWC 8 which are disposed on the input side of the AWG
144g.
Next is described a configuration of the optical TS-SW unit
configured as a spatial switch of broadcast and select type.
FIG. 108 is a basic configuration of the optical TS-SW unit 144A of
broadcast and select type. The AWG 141 demultiplexes an optical
signal inputted through wavelength multiplexing (WDM). The coupler
144r transmits the demultiplexed wavelength components to a
plurality of N.times.1 SWs (switches) 144t. The N.times.1 SWs 144t
provide control (through control) of transmission/interruption of a
signal using a semiconductor optical amplifier (SOA). One of the
N.times.1 SWs 144t is saved as a port for DROP. A coupler 142
multiplexes output from the other N.times.1 SWs 144t and outputs
from the TWC [A]1 and transmits the multiplexed outputs as a
wavelength multiplexed signal. Each if the N.times.1 SWs 144t
includes: a semiconductor optical amplifier (SOA) 144u for each
input port; a SOA 144w for each output port; and a spatial switch
144v. If the number of ports is N, the number of the SOAs to be
controlled is N.sup.2.
FIG. 109 is a diagram illustrating another example of the optical
TS-SW unit 144B of broadcast and select type. The configuration
illustrated in FIG. 108 requires a number of the SOAs 144u, 144w to
constitute the N.times.1 SWs 144t. The configuration illustrated in
FIG. 109 thus includes, instead of the N.times.1 SWs 144t
illustrated in FIG. 108, a wavelength variable filter 144x, each of
which provides control (through control) of transmission or
interruption of a signal with respect to an arbitrary wavelength,
using a wavelength filter. The configuration does not require the
AWG 144i at the prior stage. The configuration illustrated in FIG.
109 allows the number of elements which provide control on the
switches, to be reduced from N.sup.2 to N, compared to the
configuration illustrated in FIG. 108.
Seventh Embodiment
Next is described a seventh embodiment with reference to related
drawings. Referring to FIG. 110, a definition of time slot
synchronization is described.
When a time slot transmitting node (node A) and a time slot
receiving node (node B) are present, a signal transmitted from node
A arrives at node B after a delay of a propagation delay time 301AB
between nodes A, B. A start timing 301A of time slots TS1 to TS5
which operate at node A is thus made advanced from time slots TS1
to TS5 which operate at node B by the propagation delay time (plus
guard band) 301AB. This makes the time slots TS1 to TS5 which
operate at node A and the time slots TS1 to TS5 which operate at
node B to be synchronized. The time slots TS1 to TS5 operate
periodically, and a start timing of a time slot period is
hereinafter referred to as a time slot start position. Counters
each provided within nodes A, B measure an operation period and a
length of each of the time slots, by counting up for each 1 clock
of a local clock frequency.
Referring to FIG. 111, next is described a basic idea of the
present invention by exemplifying a multi-ring network (which may
also be simply referred to as a multi-ring) 302 of a unidirectional
communication.
The multi-ring 302 includes: an upper ring 303; and a plurality of
lower rings 304, which are connected to each other at node A as a
ring intersection point.
(1) A reference time slot (first time slot) 305 is made to operate
at node A as the ring intersection point and each of nodes B of the
lower rings 304.
The reference time slot 305 is a time slot synchronizing with a
time slot operating in a source node A0 existing in the upper ring
303. The source node A0 used herein is any one of a plurality of
nodes connected to a given ring and is determined as a source node.
The source node A0 corresponds to the above-described master
node.
The reference time slot can be synchronized in such a manner that:
the source node A0 transmits a synchronization frame (in which a
time value in the source node at a time of transmitting the
synchronization frame is inserted) at a timing of a reference time
slot start position in the source node A0, to the nodes other than
the source node; and, upon receipt of the synchronization frame
from the source node A0, each of the nodes other than the source
node sets the time value in the synchronization frame as a current
time of its own node and starts the reference time slot. Similarly,
upon receipt of the synchronization frame from the source node A0,
each of nodes B of the lower rings 304 starts a reference time
slot. At this time, it is necessary to deliver the synchronization
frame from the source node A0 to the nodes of the upper ring 303
other than the source node and nodes B of the lower rings 304. This
can be realized by branching the synchronization frame at each of
the nodes using an optical coupler.
(2) Node A as the ring intersection point sets a time slot for the
upper ring 303 (which may also be referred to as a second time
slot) 306 which is obtained by shifting the reference time slot
(first time slot) 305 of its own node by the synchronized offset
value (delay time), to node B on the lower ring 304 in which
transmission is performed as illustrated in TS1 indicated by an
arrow Y20. The offset value DB used herein corresponds to the
propagation delay time DB from node B to node A as the ring
intersection point shown in the multi-ring 302.
This can synchronize the time slot 306 for the upper ring 303 of
node B with the reference time slot 305 of the ring intersection
point node A. Further, node B uses the reference time slot 305 in a
downstream communication which is a transmission from the upper
ring 303 to the lower ring 304 indicated by the arrow Y20; and uses
the time slot 306 for the upper ring 303 in an upstream
communication which is a transmission as in a case of TS5 from the
lower ring 304 to the upper ring 303 indicated by an arrow Y21. TS5
used herein is a time slot into which a data is to be inserted.
This can separate, at node B, a time slot transmission (ADD) to the
upper ring 303, from a TDM control timing used for a time slot
reception (DROP) from the upper ring 303.
As described above, the time slot 306 for the upper ring of each of
nodes B on the lower ring 304 is synchronized with the reference
time slot 305 of the ring intersection point node A; and the time
slot 306 for the upper ring is used in the upstream communication
from the lower ring 304 to the upper ring 303. This makes it
possible to exchange time slots between the rings without
occurrence of time slot collision. Further, a length of a guard
band to be required can be reduced. Note that the figure also
illustrates a concept of a logical configuration in which upstream
and downstream time slots are used (arrow Y22).
Referring to FIG. 112, how to synchronize a time slot of the lower
ring 304 with a time slot of the ring intersection point node A in
a multi-ring network of a unidirectional communication is
described.
(1) Source node A0 starts a reference time slot and makes each of
nodes other than the source node synchronize with the reference
time slot. The reference time slot can be synchronized in such a
manner that: the source node A0 transmits a synchronization frame
(in which a time value in the source node at a time of transmitting
the synchronization frame is inserted) at a timing of a reference
time slot start position in the source node A0, to the nodes other
than the source node; and, upon receipt of the synchronization
frame from the source node A0, each of the nodes other than the
source node sets the time value in the synchronization frame as a
current time of its own node and starts the reference time slot.
This can synchronize the reference time slot 308 between the source
node A0 and the nodes other than the source node. Usage of the
reference time slot 308 allows ADD/DROP of a time slot between
different frames with respect to a direction of delivering the
synchronization frame.
(2) Node A as the ring intersection point sets a time slot 309 for
the upper ring which is synchronized with the reference time slot
308 of the ring intersection point node A, to each of nodes B on
the lower ring 304. In order to set the time slot 309 for the upper
ring to each of the node B on the lower ring 304, the ring
intersection point node A measures a one-round delay of the lower
ring B.
The lower ring one-round delay time is required because: on the
multi-ring 302, a time slot 309 transmitted from the node B on the
lower ring 304 arrives at the ring intersection point node A a time
D1 after; a start timing of the reference time slot of the node B
on the lower ring 304 is delayed in comparison with the reference
time slot 308 of the ring intersection point node A by a time D2;
and an addition of (D1+D2) is the lower ring one-round delay time.
The time D1 used herein means a delay time on a path heading from a
lower node (for example, B) to an upper node (for example, A). The
time D2 used herein means, in contrast, a delay time on a path
heading from the upper node A to the lower node B.
As a result of the described above, the time slot for upper ring
309 of the node B on the lower ring 304 can be synchronized with a
time slot start timing of the reference time slot 308 of the ring
intersection point node A, by starting the time slot for upper ring
309 itself by a ring one-round time with respect to a time slot
start timing of a reference time slot of its own node B on the
lower ring 304.
The lower ring one-round delay time is measured as follows: (a) The
ring intersection point node A transmits a lower ring one-round
delay measurement frame; (b) The ring intersection point node A
receives the lower ring one-round delay measurement frame; and (c)
A counter value at a time of processing (b) is subtracted from
counter value at a time of processing (a).
(3) Each the nodes B on the lower ring 304 ticks a time slot (a
time slot for upper ring) 309 which is shifted by an offset value
from a time slot start timing of the reference time slot 308 of its
own node. This can synchronize the time slot for upper ring 309 of
each of the nodes B on the lower ring 304 with the reference time
slot 308 of the ring intersection point node A. The ring
intersection point node A transmits a synchronization frame for
starting a ticking of the time slot for upper ring 309, to each of
the nodes B on the lower ring 304. At this time, the ring
intersection point node A transmits the synchronization frame with
the measured lower ring one-round delay as a time stamp added
thereto. A timing of the transmission is made to synchronize with a
start timing of a time slot period of the reference time slot after
the lower ring one-round time is measured, such that the
synchronization frame arrives at a head position of the head
position of each of the nodes B on the lower ring 304. Upon receipt
of the synchronization frame, each of the nodes B of the lower ring
304 advances the reference time slot 308 of its own node by the
lower ring one-round time described in the synchronization frame,
to thereby tick the time slot for upper ring 309. More
specifically, each of the nodes B starts a counter of a time slot
for the upper ring, by taking a value obtained by adding a time
stamp value in the synchronization frame to a reference counter
value at a time of receiving the synchronization frame, as an
initial value. Usage of the time slot for upper ring 309 enables
transmission and receipt of a time slot from the node B on the
lower ring 304 to the node A0 on the upper ring 303.
Next is described how to synchronize a reference time slot
operating in the source node A0 and a time slot used at a time of
jumping over the source node A0 (a time slot for jump) in a single
unidirectional network.
(1) The reference time slot is synchronized between all nodes. The
reference time slot can be synchronized by delivering a
synchronization frame from the source node A0 to each of the all
nodes other than the source node. A wavelength for control
different from that for data is used in communications of the
synchronization frame, to thereby ensure reachability between the
nodes.
More specifically, the source node A0 transmits the synchronization
frame at a head start position of the reference time slot of its
own node. The nodes other than the source node: receives the
synchronization frame by copying a control signal using a optical
coupler; starts a bit counter for the reference time slot from a
timing of receiving the synchronization frame; and starts a ticking
of the reference time slot. A counter is used for counting a time
slot period and a time slot length and counts up for each clock of
a local clock frequency. As a result, the reference time slot
operates with a delay of a start time of a time slot period by a
propagation delay time between the nodes, which makes it possible
to synchronize the reference time slot between the nodes. Usage of
the reference time slot allows ADD/DROP of a time slot between
different frames with respect to a direction of delivering the
synchronization frame.
(2) In the ring one-round delay measurement, the source node A0
measures one-round delay so as to synchronize time slot start
timing of time slots for jump of the nodes other than the source
node in accordance with the reference time slot of the source node
A0. The ring one-round delay measurement is required because: a
time slot transmitted from the node other than the source node
arrives at the source node A0 a time D1 after; a start timing of
the reference time slot of the node other than the source node is
delayed in comparison with the reference time slot of the source
node A0 by a time D2; and an addition of (D1+D2) is a ring
one-round delay time.
As a result of the described above, the time slot for jump of the
node other than the source node can be synchronized with a time
slot start timing of the reference time slot of the source node A,
by starting the time slot for jump itself by a ring one-round time
with respect to a time slot start timing of a reference time slot
of its own node (the node other than the source node).
The ring one-round delay time is measured as follows: (a) The
source node A0 transmits a synchronization frame; (b) The source
node receives the synchronization frame having been made one round
of a ring; and (c) A counter value at a time of processing (b) is
subtracted from counter value at a time of processing (a).
(3) Next is described how to set a time slot for jump synchronized
with the reference time slot of the source node A0. The source node
A0 transmits a synchronization frame for starting a ticking of the
time slot for jump, to the nodes other than the source node. At
this time, the source node A0 transmits the synchronization frame
with the measured one-round delay as a time stamp added thereto. A
timing of the transmission is made to be a time slot start position
of the reference time slot after the ring one-round time is
measured, such that the synchronization frame arrives at a time
slot start position of the reference time slot of the node other
than the source node.
Upon receipt of the synchronization frame, each of the nodes
advances the reference time slot of its own by the lower ring
one-round time described in the synchronization frame, to thereby
tick the time slot for jump. More specifically, the node other than
the source node starts a counter for jump, by taking a value
obtained by adding a time stamp value in the synchronization frame
to a reference counter value at a time of receiving the
synchronization frame, as an initial value. Usage of the time slot
for jump enables transmission and receipt of a time slot from the
nodes other than the source node to the source node A0.
Next is described a functional block of each of nodes with
reference to FIG. 113.
The node includes: an optical switch unit (optical time slot
switching unit) 311; a buffer unit 312; a control information
transmission unit 313; a reference TS synchronization unit 314; a
delay measurement unit 315; a plural TS management unit 316; a
counter management unit 317; an internal clock unit 318; a TS
control unit 319; a TS amount update timing calculation unit 320;
and a control information receipt unit 321. Designated at a
reference character "a" is a delay measurement result; at "b", a
clock; at "c", a reference time; at "d", a current time; a "e",
time stamp information from other node; at "f", allocation TS
information; at "g", time stamp information at each TS; at "h", a
TS transmission timing; at "i", an optical switch switching timing;
at "j", a buffer accumulation amount; at "k", a head start position
of a reference TS amount; at "l", TS change information; at "m", TS
information and TS switching timing; and at "n", head start timing
of a plurality of TSs.
The optical switch unit 311 performs ADD/DROP of a time slot.
The control information receipt unit 321 receives a control signal
subjected to DROP by the optical switch unit 311.
The buffer unit 312: includes a buffer in which a data inputted
from an external unit (not shown) is accumulated; and has a TX
(transmitter) of the buffer from which a data is transmitted to the
optical switch unit 311 and a RX (receiver) of the buffer in which
a data is received from the optical switch unit 311 and from which
the data is transmitted to the external unit.
The control information transmission unit 313 transmits a data
amount accumulated in the buffer of the buffer unit 312 and a time
counter value in the counter management unit 317, to a source
node.
The reference TS synchronization unit 314 ticks a time slot at a
prescribed period (a reference time slot) from a time set by the
source node (a time when a synchronization frame is received from
the source node).
The delay measurement unit 315: measures a propagation delay time
between the node itself and other node, based on a time stamp in
the control signal (a delay measurement frame) from other node and
a time counter value in the counter management unit 317; calculates
an inter-node propagation delay time, based on the measured
propagation delay time; and obtains an offset value for determining
a start timing of a time slot of each of the nodes.
The plural TS management unit 316 manages a time slot which is
shifted from a reference time slot of each node by a start timing
of the offset value, in accordance with the offset value from the
delay measurement unit 315. The plural TS management unit 316
stores therein a time slot position allocated to each time
slot.
The counter management unit 317: sets a time stamp in the
synchronization frame received from the source as an initial time
counter value; and increments the time counter value from a time
when the synchronization frame is received, in accordance with a
calculate of the internal clock unit 318.
The internal clock unit 318 supplies the counter management unit
317 with a clock for advancing the time counter value present in
the counter management unit 317.
The TS control unit 319: compares the time counter value in the
counter management unit 317 with a timing value described in a time
slot processing scenario, in accordance with the time slot
processing scenario in the plural TS management unit 316; and
provides control of a time slot transmission and a time slot switch
operation on the optical switch unit 311 and the buffer unit 312.
Note that control of transmission or the like of a delay
measurement frame and a frame for plural time slot start to be
described hereinafter is provided by the TS control unit 319.
TS amount update timing calculation unit 320 calculates a time slot
amount which is common to a plurality of time slots and switching
timing of the time slots.
Input/output of the optical switch unit 311 and a (transmission)
and a RX (receipt) of the buffer unit 312 are operated in
accordance with at least one time slot.
Next are described definitions of an M-C, a Sub M-C, and an S-C
taking a topology in a unidirectional communication and a two-step
ring as an example, with reference to FIG. 114. Herein, an M-C 331
is a source node as a master node. SubM-Cs 332a, 332b
(collectively, 332) are ring intersection point nodes as sub master
nodes. S-Cs 333a to 333c (collectively, 333) are nodes as slave
nodes (which correspond to the above-described optical switch nodes
other than the master node).
The M-C 331 is a representative node (source node). Only one unit
thereof is present in a optical network system.
The M-C 331 mainly serves as follows.
The M-C 331: transmits a synchronization frame for starting a time
slot of each of the nodes 332, 333; and measures a propagation
delay time and calculates an offset value between the nodes 332,
333.
The SubM-C 332 mainly serves as follows.
The SubM-C 332 transmits a plural time slots start frame which
makes a new time slot start with a shift by the calculated offset
value, to the time slot of each of the nodes 332, 333 which has
already been operating. The SubM-C 332 is located at a ring
intersection point and controls the optical switch unit 311 (see
FIG. 113).
That is, the SubM-C 332 ticks a plurality of time slots in
accordance with an instruction from the M-C 331. The SubM-C 332
controls the optical switch unit 311 of its own in accordance with
a time slot allocated by the M-C 331.
The S-C 333 is a node which is located off the ring intersection
point and controls the optical switch unit 311 and the buffer unit
312 (see FIG. 113).
The S-C 333 mainly serves as follows.
The S-C 333 ticks a plurality of time slots in accordance with an
instruction from the M-C 331. The S-C 333 also controls the optical
switch unit 311 and the buffer unit 312 of its own in accordance
with a time slot allocated by the M-C 331.
Next is described how the source node 331 sets a time slot start
timing with reference to FIG. 115A and FIG. 115B. Herein, in an
optical network system of FIG. 115A: an upper ring 335 is connected
to two lower rings 336a, 336b by two nodes, that is, SubM-Cs (ring
intersection point nodes) 332a, 332b, respectively; the upper ring
335 includes the source node 331 and an S-C 333c which is a node
(an optical switch node); and the lower rings 336a, 336b include
nodes (optical switch nodes) 333a, 333b, respectively. Inter-node
propagation delay times are assumed to be, as illustrated in FIG.
115B: "150" between the source node 331 and the node 332a; and
"200" between the node 332a and the node 333b. The source node 331
may also be simply referred to as the node 331; the ring
intersection point node 332, the node 332; and the optical switch
node 333, node 333.
The setting of the time slot start timing is performed so as to
shift a start timing of a time slot periodically operating at each
of the nodes 331 to 333, by a propagation delay time between each
of the nodes 332, 333 and the source node 331, respectively.
One source node 331 is provided in the optical network system. The
source node 331 transmits a synchronization frame to each of the
nodes other than the source node, that is, the nodes 332a, 333b so
as to determine a time slot start timing t10, as indicated by
arrows Y25, Y26, respectively. Each of the nodes 332, 333 other
than the source node starts operating of a time slot thereof upon
receipt of the synchronization frame. Thus, the start timing of the
time slot operating in each of the nodes 332a, 333b other than the
source node is shifted by the propagation delay times of "150, 200"
between each of the nodes 332a, 333b and the source node 331,
respectively.
That is, the start timing of the time slot synchronized with a
burst transmission period of the node 332a is a time t11a which is
a time shifted by a transmission delay of "150" from the timing
time t10 of the source node 331. Further, the start timing of the
time slot synchronized with a burst transmission period of the node
333b is a time t13a which is shifted by "150+200=350" from the
transmission delay from the timing time t10.
With respect to the reference time slot, a time slot transmitted in
a direction from the source node 331 toward arrows Y25, Y26 in FIG.
115B is hereinafter referred to as a forward direction time
slot.
Next is described how to set a time at each of nodes with reference
to FIG. 116.
The source node 331: adds a current time of its own to a
synchronization frame as a time stamp; and transmits the
synchronization frame to each of the nodes 332, 333 other than the
source node. Upon receipt of the synchronization frame, each of the
nodes 332, 333 other than the source node sets the time stamp in
the synchronization frame as a current time of its own node. As a
result, a time at each of the nodes 332, 333 other than the source
node is set with a shift by a propagation delay time from the
source node 331.
At this time, a wavelength for control which is different from that
for data is used, because the synchronization frame is transmitted
to each of the nodes 332, 333 via the optical switch unit 311 which
is active.
To ensure that each of the nodes receives the synchronization
frame, as illustrated in a box 324, the optical coupler 322 or the
like may copy a wavelength for control for each of the nodes 332,
333. Or, as illustrated in a box 325, the synchronization frame may
be transmitted P-to-P (Peer to Peer) using different wavelengths
for control to the nodes 332, 333. That is, a plurality of nodes in
equal relationship in a network may be directly P-to-P connected to
each other, in which a data is transmitted and received.
Next is described an advantageous effect of the setting of a time
slot start timing as illustrated in FIG. 115, with reference to
FIG. 117A and FIG. 117B.
As indicated by a time t11 in FIG. 117B, a time slot transmission
is performed by setting a time slot start timing by the source node
331 in a direction same as that of the synchronization frame, which
is indicated by, in FIG. 117B, an obliquely downward arrow Y28,
and, in FIG. 117A, the counterclockwise arrow Y28. Various
operations become possible by controlling the buffer unit 312 and
the optical switch unit 311 consistent with the forward direction
time slot. Such operations include, as illustrated in FIG. 117B,
ADD at TS2 of the node 331, THRU at TS2 of the node 332a; and DROP
at TS2 of the node 333b.
Next is described how to measure a propagation delay time between
adjacent nodes with reference to FIG. 118.
The source node 331 transmits a synchronization frame to which a
current time (T1) in the source node 331 is given as a time stamp
as indicated in a bix 118e of FIG. 118, to each of the nodes 332,
333 other than the source node as indicated by an arrow Y31.
Each of the nodes 332, 333 other than the source node sets the time
stamp in the synchronization frame received from the source node
331 as a current time T1 of its own node. After a processing time
to which is set with a parameter, each of the nodes 332, 333
transmits a delay measurement frame to which a current time T2
inside its own node is given as a time stamp, to the source node
331 as indicated by an arrow Y32. Explanations on the transmission
are described also in a box 118a.
At this time, the delay measurement frame is transmitted through a
path through which the source node 331 transmits the
synchronization frame. Passing the delay measurement frame through
the same path as the synchronization frame makes it possible to
measure a propagation delay time between the nodes 331 to 333. Note
that when the delay measurement frame is transmitted, there is a
possibility of colliding with the delay measurement frame from each
of the nodes 331 to 333. Thus, the delay measurement frame is
repeatedly transmitted at random timing. Or, the delay measurement
frame is transmitted in accordance with a time slot allocated to
each of the nodes 331 to 333. Note that a wavelength for control
which is different from that for data is used, because the delay
measurement frame is transmitted to each of the nodes 332, 333 via
the optical switch unit 311 which is active.
The source node 331 calculates, from the time T3 inside the source
node 331 at a time of receiving the delay measurement frame and the
time T2 of the time stamp inside the delay measurement frame, a
propagation delay time (=(T3-T2)+2) from the source node 331 to
each of the nodes 332, 333. The calculation includes a division by
2 because a one-way propagation delay time is calculated as
indicated in a box 118b.
As described above, the source node 331: measures the propagation
delay time between the nodes 332, 333 other than the source node;
and calculates a propagation delay time between adjacent nodes,
based on a result of the measurement. For example, the source node
331: calculates a difference between a propagation delay time
between the nodes 331 and 333b and a propagation delay time between
the nodes 331 and 332a; and determines the difference as a
propagation delay time between the adjacent nodes 332a, 333b. A
conceptual diagram and an explanation thereof of the propagation
delay times measured and calculated as described above are
illustrated in boxes 118d, 118c of FIG. 118, respectively. In the
box 118d, reference characters A to E are given to nodes (optical
switch nodes) other than a master node as the source node.
The source node 331 also measures a ring one-round delay time so as
to use for a time slot for communication jumping over the source
node. The ring one-round delay time is measured as follows: (a) the
source node 331 transmits a transmits a ring one-round delay
measurement frame; (b) the source node 331 receives the ring
one-round delay measurement frame after making one round of the
one-round; and (c) A counter value at a time of processing (b) is
subtracted from a counter value at a time of processing (a).
The ring intersection point node 332 measures a lower ring
one-round delay time so as to be used for a time slot for
communication from the node 333a, 333b on lower rings 336a, 336b to
the node 333c on the upper ring 335. The lower ring one-round delay
time is measured as follows: (a) the ring intersection point node
332 transmits a lower ring one-round delay measurement frame; (b)
the ring intersection point node 332 receives the ring one-round
delay measurement frame after making one round on the lower ring;
and (c) A counter value at a time of processing (b) is subtracted
from a counter value at a time of processing (a).
Next is described how to measure a propagation delay time with
reference to FIG. 119A and FIG. 119B.
Referring to FIG. 119A, a case in which a path of a synchronization
frame is symmetrical to a path of a delay measurement frame is
described.
Each of the nodes 332, 333 other than the source node: sets a time
stamp in the synchronization frame as a current time of its own
node; and transmits a delay measurement frame to which the time (or
a time ticked from the time in accordance with a local clock of
each of the nodes) is added as a time stamp, to the source node,
through a path through which the synchronization frame is
transmitted in a direction indicated by an arrow Y30, in a
direction opposite thereto as indicated by an arrow Y31. At this
time, to ensure that the delay measurement frame is received by the
source node 331, an optical coupler 322 is disposed in a path
difference from that of the optical switch unit 311, and the delay
measurement frame is transmitted.
The source node 331 obtains a difference between the time stamp in
the received delay measurement frame and a time inside thereof when
the source node 331 itself receives the delay measurement frame, to
thereby measure a round-trip propagation delay time between the
nodes 332, 333.
Referring to FIG. 119B, a case in which a path of a synchronization
frame is asymmetrical to a path of a delay measurement frame is
described.
Each of the nodes 332, 333 other than the source node: sets a time
common to the nodes (including the source node) 331 to 333 (common
time) (for example, using a GPS receiver 324); and transmits a
delay measurement frame to which the common time is added as a time
stamp, to the source node 331, through a path through which the
synchronization frame is transmitted in a direction indicated by an
arrow Y30, in the same direction as indicated by an arrow Y32.
The source node 331 obtains a difference between the time stamp in
the received delay measurement frame and a common time inside
thereof when the source node 331 itself receives the delay
measurement frame, to thereby measure a one-way propagation delay
time between the nodes 332, 333.
(A) and (B) as follows are contemplated herein based on the
operations with reference to FIG. 119A and FIG. 119B as illustrated
above.
(A) If a plurality of the nodes 331 to 333 share a wavelength for
control, each of the nodes 331 to 333 continues to transmit a delay
measurement frame at random timing, to thereby make the delay
measurement frame from each of the nodes 332, 333 arrive at the
source node 331. In and after the second measurement, a time slot
for control which is synchronized based on a delay time between the
source node 331 and each of the nodes 332, 333 is used, thus
allowing collision of different delay measurement frames between
the nodes 332, 333 from being prevented.
(B) The delay measurement frame may be P-to-P transmitted to the
source node using different wavelengths for control for each of the
nodes 331 to 333.
The source node 331: transmits or receives a synchronization frame
to and from itself using a wavelength for control; and measures a
propagation delay time for one round on an upper ring, based on a
time stamp in the synchronization frame and a time of its own.
The ring intersection point node 332: transmits or receives a
synchronization frame to and from itself using a wavelength for
control; and measures a propagation delay time on the upper ring
335 or one round on the lower ring 336, based on a time stamp in
the synchronization frame and a time of its own. Note that the ring
intersection point node 332 notifies the source node 331 of the
propagation delay time for one round on the lower ring 336.
The source node 331 calculates a difference between each of
propagation delay times between each of the nodes 332, 333 other
than the source node and the source node 331, to thereby calculate
a propagation delay time between the nodes 332, 333 other than the
source node.
Next is described how to measure a propagation delay time for one
round on a ring with reference to FIG. 120.
Each of the source node 331 and the ring intersection point nodes
332a, 332b transmits or receives a synchronization frame to and
from itself, as illustrated in a box 120a; and calculates a
difference between a current time of its own at a time of receiving
the synchronization frame and a time stamp in the synchronization
frame, to thereby measure a propagation delay time for one round on
the ring.
Note that the synchronization frame is transmitted in such a manner
that: an exclusive wavelength is allocated for the transmission to
ensure that the node receives the synchronization frame from
itself; or the node transmits the synchronization frame in
accordance with a time slot allocated to the node itself.
Next is described a timing separation between an ADD onto the upper
ring 335 illustrated in FIG. 120 and a DROP onto the lower ring
336, taking a propagation delay into account, with reference to
FIG. 121. In this case, ADD interfaces as much as the number of
time slots are provided. Or, one ADD interface and a variable time
slot are provided.
The source node 331 sets a plurality of time slots to each of the
nodes 332, 333 other than the source node, based on a propagation
delay time between the nodes 332, 333, taking into account
propagation delays corresponding to paths used.
The source node 331 transmits a plural time slots start frame in
which an offset value from a forward direction time slot having
already been operating in each of the nodes 332, 333 other than the
source node is described, to each of the nodes 332a, 333b other
than the source node, as indicated by an arrow Y33 starting from a
time t11.
Upon receipt of the plural time slots start frame, each of the
nodes 332a, 333b other than the source node starts ticking a time
slot with a shift from the forward direction time slot by the
offset value as indicated by an arrow Y34 (a time slot for upper
ring), which is described in a box 121f.
The number of time slots require for each of the nodes 332, 333 is
2.times..PI.i=1, N (the number of communication paths at a ring of
each step).
In the expression described above, i=the number of steps of a ring
to which each of the rings belongs, counting from the upper
ring.
For example, in a case of a two-step ring of a unidirectional
communication (a data arrives at each of the nodes
unidirectionally), the number of time slots of the upper ring and
the lower ring are (1) and (2) as follows, respectively.
(1) the number of time slots of upper ring is two (a forward
direction time slot and a time slot for ring one round).
(2) the number of time slots of the lower ring is four (a forward
direction time slot, a time slot for ring one round, a time slot
for forward direction time slot of the upper ring, and a time slot
for ring one round time slot of the upper ring).
Next is described a time slot directed from the lower ring 336 to
the upper ring 335 with reference to FIG. 122A and FIG. 122B.
A case is assumed in which ADD is performed from the node 333b on
the lower ring 336b to a forward direction time slot of the node
332a on the upper ring 335. Let "200" be an internode distance of a
counterclockwise path from the node 332a to the node 333b (a
propagation delay time be D45 corresponding thereto). Let "50" be
an internode distance of a counterclockwise path from the node 333b
to the node 332a (a propagation delay time be D54 corresponding
thereto).
(1) a time slot start timing of the node 333b on the lower ring
336b is delayed from the node 332a on the upper ring 335 by the
propagation delay time D45, as indicated by times t11a and t13a of
122B.
(2) A data in a time slot transmitted from the lower ring node 333b
arrives at the upper ring node 332a by the propagation delay time
D54, as indicated by an arrow Y35.
In light of the above-described (1) and (2), a time slot whose
start timing is advanced by D45+D54 (=propagation delay time for
one round on the lower ring 1) from the forward direction time slot
operating in the lower ring node 333b, as indicated by an arrow Y36
(a time slot for upper ring) is used. This makes it possible to
perform ADD at the node 333b onto the upper ring.
Next are described various types of time slots required when a
bidirectional communication (a data in a time slot arrives both
clockwise and counterclockwise with respect to a source node) is
performed on a multi-ring, with reference to FIG. 123A and FIG.
123B.
Definitions of a propagation delay time are as follows as
illustrated in FIG. 123A.
Dru: a propagation delay time for one round on an upper ring. Dn: a
propagation delay time between M-C to S-C on the upper ring. Ds: a
propagation delay time between M-C to Sub M-C on the upper ring.
Drl: a propagation delay time for one round on a lower ring. Dp: a
propagation delay time between Sub M-C to S-C on the lower
ring.
Next is described FIG. 123B. In FIG. 123B, the source node 331 is
described as an M-C. In explanations of FIG. 123A and FIG. 123B t:
time slot period and t0: time slot length.
[1] A forward direction time slot is: on the upper ring, a time
slot delayed from a forward direction time slot inside an M-C by a
time Dn; and, on the lower ring, a time slot delayed from the
forward direction time slot inside the M-C by a time Ds+Dp.
[2] A backward direction time slot is, on the upper ring, a time
slot advanced from the forward direction time slot inside its own
node by a time 2Dn.
Or, the backward direction time slot is a time slot delayed from
the time slot in the forward direction inside its own node by a
time t-MOD (2Dn, t) (Herein, MOD (A, B) represents a residue of
A+B. For example, MOD (3, 2)=1, and MOD (2, 7)=2. Ditto below.)
Or, the backward direction time slot is a time slot delayed from
the time slot in the forward direction inside its own node, by a
time t0-MOD (2Dn, t0).
The backward direction time slot is, on the lower ring, a time slot
advanced from the time slot from the forward direction time slot
inside its own node by a time 2(Ds+Dp).
Or, the backward direction time slot is a time slot delayed from
the time slot in the forward direction inside its own node, by a
time t-MOD (2(Ds+Dp), t).
Or, the backward direction time slot is a time slot delayed from
the time slot in the forward direction inside its own node, by a
time t0-MOD (2(Ds+Dp), t0).
[3] A forward direction jump time slot is, on the upper ring, a
time slot advanced from the time slot in the forward direction
inside its own node, by a time Dru.
Or, the forward direction jump time slot is a time slot delayed
from the time slot in the forward direction inside its own node, by
a time t-MOD (Dru, t).
Or, the forward direction jump time slot is a time slot delayed
from the time slot in the forward direction inside its own node, by
a time t0-MOD (Dru, t0).
The forward direction jump time slot is, on the lower ring, a time
slot delayed from the time slot in the forward direction inside its
own node, by a time Drl.
Or, the forward direction jump time slot is a time slot delayed
from the time slot in the forward direction inside its own node, by
a time t-MOD (Drl, t).
Or, the forward direction jump time slot is a time slot delayed
from the time slot in the forward direction inside its own node, by
a time t0-MOD (Drl, t0).
[4] A backward direction jump time slot is, on the upper ring, a
time slot advanced from the time slot in the forward direction
inside its own node, by a time 2Dn-Dru.
Or, the backward direction jump time slot is a time slot delayed
from the time slot in the forward direction inside its own node, by
a time t-MOD (2Dn-Dru, t).
Or, the backward direction jump time slot is a time slot delayed
from the time slot in the forward direction inside its own node, by
a time t0-MOD (2Dn-Dru, t0).
The backward direction jump time slot is, on the lower ring, a time
slot advanced from the time slot in the forward direction inside
its own node, by a time 2(Ds+Dp)-Drl.
Or, backward direction jump time slot is a time slot delayed from
the time slot in the forward direction inside its own node, by a
time t-MOD (2(Ds+Dp)-Drl, t).
Or, the backward direction jump time slot is a time slot delayed
from the time slot in the forward direction inside its own node, by
a time t0-MOD (2(Ds+Dp)-Drl, t0).
[5] A time slot for upper ring forward direction jump time slot is,
on the lower ring, a time slot advanced from the time slot in the
forward direction inside its own node, by a time Dru+Drl.
Or, the time slot for upper ring forward direction time slot for
jump is, on the lower ring, a time slot delayed from the time slot
in the forward direction inside its own node, by a time t-MOD
(Dru+Drl, t).
Or, the time slot for upper ring forward direction time slot for
jump is, on the lower ring, a time slot delayed from the time slot
in the forward direction inside its own node, by a time t0-MOD
(Dru+Drl, t0).
[6] A time slot for upper ring backward direction time slot for
jump is, on the lower ring, a time slot advanced from the time slot
in the forward direction inside its own node, by a time
2(Ds+Dp)-(Dru+Drl).
Or, the time slot for upper ring backward direction time slot for
jump is a time slot delayed from the time slot in the forward
direction inside its own node, by a time t-MOD (2(Ds+Dp)-(Dru+Drl),
t).
Or, the time slot for upper ring backward direction time slot for
jump is a time slot delayed from the time slot in the forward
direction inside its own node, by a time t0-MOD
(2(Ds+Dp)-(Dru+Drl), t0).
Next is described a time slot (in a forward direction) used on a
single ring network with reference to FIG. 124A to FIG. 124C. A
system configuration herein is assumed to include an M-C 351 and
S-Cs 352, 353, and 355, which are ring connected via a transmission
path 357. It is basically intended herein that each of the nodes
352 to 354 ticks a time slot in accordance with a time slot
operating in the M-C 351.
FIG. 124A is a diagram illustrating a case of a forward direction
communication as indicated by an arrow Y41, in which the time slots
of the nodes 351 to 354 are all forward direction time slots 358
because there is no jump communication which jumps over the M-C
351. The jump communication in the forward direction communication
used herein means that a signal passes between the M-C 351, which
is the source node indicated by a bidirectional arrow Y42 of FIG.
124C, and the S-C 354 in a forward direction as indicated by an
arrow Y43. In other words, the jump communication in the forward
direction communication is a jump communication from a node 354
side to the source node (M-C) 351.
FIG. 124B is a diagram illustrating a case in which a jump over the
M-C 351 is present, as indicated by an arrow Y44. Time slots of the
nodes 353, 354 each of which jumps over the M-C 351 are forward
direction jump time slots 359. The others are forward direction
time slots 358.
Next is described a time slot (in a backward direction) used on a
single ring network with reference to FIG. 125A to FIG. 125C. It is
basically intended herein that each of the nodes 352 to 354 ticks a
time slot in accordance with a time slot operating in the M-C
351.
FIG. 125A is a diagram illustrating a case of a backward direction
communication as indicated by an arrow Y45, in which the time slots
of the nodes 351 to 354 are all backward direction time slots 361
because there is no jump communication which jumps over the M-C
351. The jump communication in the backward direction communication
used herein means a signal passing between the M-C 351, which is
the source node indicated by a bidirectional arrow Y42 of FIG.
125C, and the S-C 354 in a backward direction as indicated by an
arrow Y46. In other words, the jump communication in the backward
direction communication is a jump communication from the source
node (M-C) 351 to the node 354 side.
FIG. 125B is a diagram illustrating a case in which a jump over the
M-C 351 is present, as indicated by an arrow Y47. A time slot of
the node 354 which jumps over the M-C 351 is a backward direction
jump time slots 362. The others are backward direction time slots
361.
Thus, in the case of the single ring network, the source node 351
determines an offset value to be set to the node (which may also be
referred to as a specific node) 354 which needs to tick a time slot
other than the forward direction time slot, from among the nodes
352 to 354 other than the source node, taking into account a
direction of a time slot and presence or absence of a jump over the
source node 351.
Next is described a time slot (in a forward direction) used on a
multi-ring network with reference to FIG. 126A to FIG. 126D. A
system configuration herein is assumed to: include an M-C 351 and
S-Cs 352, 353, and 355, which are ring connected via a transmission
path 357; and the upper ring 357 is connected to a lower ring 377
via a SubM-C 371 which is a ring intersection point node; and the
lower ring 377 is connected to S-Cs 372, 373. It is basically
intended herein that each of the nodes 352, 353, and 371 to 373
ticks a time slot in accordance with a time slot operating in the
M-C 351.
FIG. 126A is a diagram illustrating a case of a forward direction
communication as indicated by an arrow Y51, in which there is a
communication from the lower ring 377 to the upper ring 357. A time
slot of the node 373 on the lower ring 377 is a time slot for
forward direction jump time slot 378, and the others are forward
direction time slots 358.
The jump communication from the lower ring 377 to the upper ring
357 in the forward direction communication used herein means that
the S-C 373 which is a node on the lower ring 377 indicated by a
bidirectional arrow Y42b of FIG. 126D, and the SubM-C 371, in a
forward direction as indicated by an arrow Y52. That is, as
illustrated in FIG. 126B, a time slot of the node 373 on the lower
ring 377 is the time slot for upper ring forward direction jump
time slot 378. Note that, as illustrated in the same arrow Y52 of
FIG. 126D, in a case where a signal passes between the S-C 353 and
the M-C 351 which are the nodes on the upper ring 357 indicated by
a bidirectional arrow Y42a, in a forward direction, the M-C 351
performs a jump communication (a forward direction jump
communication).
FIG. 126B is a diagram illustrating a case in which a jump from the
lower ring 377 to the upper ring 357 and a jump over the M-C 351
are present, as indicated by an arrow Y53. Time slots of the nodes
371, 353 each of which jumps over the M-C 351 are forward direction
jump time slots 377a, 377b. A time slot of the node 373 which jumps
over the lower ring 377 is a time slot for upper ring forward
direction jump time slot 378. The other time slots are forward
direction time slots 376.
FIG. 126C is a diagram illustrating a case in which a jump over the
M-C 351 and a communication from the upper ring 357 to the lower
ring 377 are present as indicated by an arrow Y54. A time slot of
the node 353 on the upper ring 357 which jumps over the M-C 351 is
a forward direction jump time slot 377b. The others are the forward
direction time slots 376.
In a case other than the described above, in which a communication
from the upper ring 357 to the lower ring 377 is present, but a
jump over the M-C is not present, all the time slots are forward
direction time slots 376.
Next is described a time slot (in a backward direction) used in a
multi-ring network with reference to FIG. 127A through FIG. 127D.
It is basically intended herein that each of the nodes 352, 353,
and 371 to 373 ticks a time slot in accordance with a time slot
operating in the M-C 351.
FIG. 127A is a diagram illustrating a case in which a communication
from the upper ring 352 to the lower ring 377 is present in a
backward communication, as indicated by an arrow Y55. A time slot
of the node 373 on the lower ring 377 is a backward direction jump
time slot 381. The others are backward direction time slots
382.
The jump communication from the upper ring 357 to the lower ring
377 in the backward direction used herein means that the SubM-C 371
which is a node on the upper ring 357 indicated by a bidirectional
arrow Y42b of FIG. 127D, and the S-C 373 on the lower ring 377, in
a backward direction as indicated by an arrow Y56. That is, as
illustrated in FIG. 127B, a time slot of the node 373 on the lower
ring 377 is the time slot for upper ring backward direction jump
time slot 383. Note that, as illustrated in the same arrow Y56 of
FIG. 127D, in a case where a signal passes between the S-C 353 and
the M-C 351 which are the nodes on the upper ring 357 indicated by
a bidirectional arrow Y42a, in a backward direction, the M-C 351
performs a jump communication (a backward direction jump
communication).
FIG. 127B is a diagram illustrating a case in which a jump from the
upper ring 357 to the lower ring 377 and a jump over the M-C 351
are present, as indicated by an arrow Y57. A time slot of the node
373 on the lower ring 377 is a time slot for upper ring backward
direction time slot for jump 383. Time slots of the node 353 on the
upper ring 357 and the SubM-C 371 which jump over the M-C 351 are
backward direction jump time slots 384a, 384b, respectively. The
others are backward direction time slots 382.
FIG. 127C is a diagram illustrating a case in which a communication
from the lower ring 377 to the upper ring 357, and a jump over the
M-C 351 are present, as indicated by an arrow Y58. A time slot of
the node 353 on the upper ring 357 which jumps over the M-C 351 is
a backward direction jump time slot 384. The others are backward
direction time slots 382.
Further, in a case other than the described above in which: a
communication from the lower ring 377 to the upper ring 357 is
present, but a jump over the M-C is not present, all the time slots
from the lower ring 377 to the upper ring 357 are backward
direction time slots 382.
Thus, in the case of the single ring network, the source node 351
determines an offset value which is to be set to the nodes
(specific nodes) 353, 373 which needs to tick a time slot other
than the forward direction time slot, from among the nodes 352,
353, and 371 to 354 other than the source node, taking into
account: a direction of a time slot; presence or absence of a jump
over the source node 351; presence or absence of a jump from the
upper ring 357 to the lower ring 377; and presence or absence of a
jump from the lower ring 377 to the upper ring 357.
Next is described an operating sequence when an operation of
delivering a time counter value at the M-C [1], with reference to
FIG. 128. The operation herein is assumed to be performed in a
system in which, in a multi-ring network illustrated in FIG. 123A:
an M-C [1] and an S-C [2] are connected to an upper link; an upper
ring and a lower ring are relay connected via SubM-Cs [3], [4]; and
an S-C [5] is connected to the lower ring.
Propagation delay times D1 to D4 also illustrated in FIG. 128 each
represent: a propagation delay time between the M-C [1] and the S-C
[2] as D1; between the M-C [1] and the SubM-C [3] as D2; between
the M-C [1] and the SubM-C as D3; and between the SubM-C [3] and
S-C [5] as D4.
Upon input of a command, the M-C [1]: starts counting of a time
counter value of the counter management unit 317 (see FIG. 113) in
the M-C [1] itself; and also starts ticking of both a forward
direction time slot for control and a forward direction time slot
for data. In FIG. 128, an initial value of the time counter value
is "100", and the time slot for control starts at TS1. The time
slot is incremented according to a count up of the time counter
value such as, at "200", TS2, and, at "300", TS3. Note that, in
addition to the time slot for control, ticking of the time slot for
data not shown is simultaneously performed.
Next is described an operating sequence when an operation of
delivering an initial time counter value at the M-C [1] is set,
with reference to FIG. 129.
The M-C [1] sets how an initial time counter value is delivered to
each of nodes [2] to [5] other than the M-C. The initial time
counter value is delivered by containing in command setting
information in a synchronization frame. In the command setting
information: a number of a forward direction time slot for control
which is used in delivering the initial time counter value; a
destination MAC address, a destination controller ID; a number of a
time slot for allocation control which is allocated used for
responding to the initial time counter value are set. Note that the
initial time counter value may be contained in a time counter
operation start command.
Next is described an operating sequence when an initial time
counter value in the M-C [1] is delivered to an upper ring, with
reference to FIG. 130.
The M-C [1] delivers a synchronization frame to which an
appropriate initial time counter value such as "100, 200, 300, . .
. " at the forward direction time slot for control are given as a
time stamp, to each of the nodes [2] to [5] other than the M-C.
For example, in transmitting at the forward direction time slot for
control TS3, the M-C [1]: adds a time stamping processing delay
time (for example, 1) to a head of the time counter value "300" of
the forward direction time slot for control TS3; and gives a value
obtained by the addition "300+1=301" as a time stamp. The time
stamping processing delay time used herein is a time required for a
processing of giving a time stamp. The obtained value "301" is
transmitted to the SubM-C [3] as indicated by an arrow Y61.
In this case, a start time counter value of the forward direction
time slot for control is the head of the counter value "300" of the
forward direction time slot for control which has been used for the
transmission. A start time slot number of the forward direction
time slot for control is "TS3" which is a time slot number of the
forward direction time slot for control corresponding to the SubM-C
[3]. A start time counter value of a forward direction time slot
for data is "450", which is a value of a counter head as a boundary
of a forward direction time slot for data immediately after the
forward direction time slot for control used for the
transmission.
A time slot number of the forward direction time slot start for
data is "TS2" which is a forward direction time slot for data
corresponding to the SubM-C [3].
Next is described an operating sequence when an initial time
counter value in the SubM-C [3], [4] on the upper ring are
received, with reference to FIG. 131.
Upon receipt of the synchronization frame described with reference
to FIG. 130 described above, the SubM-C (for example, [3]):
subtracts "1" as a circuit processing delay time until the initial
time counter value is transmitted, from the time counter value
"301" in the synchronization frame; and gives a value of
"301-1=300" obtained by the subtraction to the time counter value
of its own node. The subtraction of "1" is performed because, when
the M-C [1] transmits the synchronization frame, "1" is added to
the time counter value as the time stamping processing delay time,
which allows an accurate counter value of "300" to be obtained.
The SubM-C [3] also receives the start time counter value of "450"
of the forward direction time slot for data, which is also
ticked.
Next is described an operating sequence when a setting of delivery
of an initial time counter value in the M-C [1] to a lower ring is
performed, with reference to FIG. 132.
The M-C [1] delivers a synchronization frame to which an initial
time counter value is given as a time stamp at a forward direction
time slot for control, to each of the nodes [2] to [4] other than
the M-C [1]. The S-C [2] starts a counterclockwise time slot
(including a time slot for data). Note that each of the SubM-Cs
[3], [4], and S-C [5] simultaneously ticks a time slot for data, in
addition to the time slot for control.
The M-C [1] simultaneously delivers synchronization frames both
clockwise and counterclockwise in some cases.
Continued is description of the operating sequence when an initial
time counter value in the M-C [1] is delivered to the lower ring,
with reference to FIG. 133.
Upon receipt of the synchronization frame to which the initial time
counter value is given as the time stamp delivered from the M-C
[1], each of the nodes [2] to [5] other than the M-C uses a forward
direction time slot for control in responding to the delivered
initial time counter value.
For this purpose, the M-C [1] allocates time slots for control
having lower numbers in order from nearest to farthest from the M-C
[1], to each of the nodes [2] to [5] other than the M-C on the
upper ring, as indicated by arrows Y63, Y64, Y65.
The M-C [1] also allocates a slot having a lower number from among
the time slots for control other than the time slot for control
allocated on the upper ring, in order from nearest to farthest from
the M-C [1] or the SubM-Cd [3], [4] (for example, [5]), to the
nodes on the lower ring, as indicated by an arrow Y66.
Note that each of the SubM-Cs [3], [4] is assumed to previously
obtain a lower ring topology and a controller ID and set the
previously obtained information using a command. Each of the
SubM-Cs [3], [4] is also assumed to deliver an initial time counter
value to the lower ring at a timing within a period starting from
receipt of the initial time counter value.
Each of the SubM-Cs [3], [4] ticks the time slot for data, in
addition to the forward direction time slot for control.
Next is described an operating sequence when the S-Cs [5], [6] on
the lower ring respond times, with reference to FIG. 134. Herein,
the S-C [6] is assumed as a node connected to a lower ring to which
the S-C [5] is connected.
Each of the S-Cs [5], [6] on the lower ring transmits a delay
measurement frame to which the initial time counter value of its
own node is give n as a time stamp, to the SubM-C [3], using
forward direction time slots for control TS7, TS8 allocated from
the M-C [1] to its own node, as indicated by arrows Y67, Y68,
respectively. Note that each of the S-Cs [5], [6] responds the
initial time counter value to the SubM-C [3] at a timing within a
period starting from receipt of the initial time counter value.
Each of the S-Cs [5], [6] adds a circuit processing delay time from
the time counter value to the transmission of the initial time
counter value (for example, 1) and takes the obtained sum as a time
counter value of its own node.
Next is described an operating sequence when the SubM-C [3]
transfers the times responded by the S-C [5], [6], with reference
to FIG. 135.
Upon receipt of the delay measurement frame to which the S-C [5] on
the lower ring has given the initial time counter value as a time
stamp, as indicated by an arrow Y67, the SubM-C [3] measures a
propagation delay time as indicated in a box 135a. The SubM-C [3]
also transmits the delay measurement frame to which the S-C [5] has
given the initial time counter value as the time stamp, to the M-C
[1] at a time slot "TS12" as indicated by an arrow Y69, using the
forward direction time slot for control allocated from the M-C [1]
to the SubM-C [3] itself. After the transmission, if the SubM-C [3]
newly receives another initial time counter value from the S-C [6]
on the lower ring as indicated by an arrow Y68, the SubM-C [3]
transmits the new initial time counter value at a forward direction
time slot for control allocated in the next period.
Next is described an operating sequence when the SubM-C [3]
transfers the times responded by the S-C [5], with reference to
FIG. 136A and FIG. 136B. Note that FIG. 136A is a configuration
diagram illustrating a multi-ring network in which reference
numerals [1] to [5] are given to respective nodes.
The SubM-C [3] delivers a synchronization frame which is destined
for the S-C [5] on the lower ring and to which an initial time
counter value is given as a time stamp, at a time slot "T59"
indicated by an arrow Y71. After the synchronization frame makes
one round of the lower ring and returns to the SubM-C [3], the
SubM-C [3] performs DROP to the synchronization frame. The SubM-C
[3] thereby measures a propagation delay time for one round on the
lower ring as indicated in a box 136a.
Further, the SubM-C [3] receives a delay measurement frame to which
the S-C [5] on the lower ring has given an initial time counter
value as a time stamp, from the S-C [5]. The SubM-C [3] then
transmits a delay measurement frame to which the initial time
counter value of the S-C [5] has been given as a time stamp, to the
M-C [1] as indicated by an arrow Y72, using a forward direction
time slot for control allocated from the M-C [1] to the SubM-C [3]
itself. After the transmission, if the SubM-C [3] newly receives
another initial time counter value from the S-C on the lower ring,
the SubM-C [3] transmits the new initial time counter value at a
forward direction time slot for control allocated in the next
period.
Next is described a timing of generating a time slot suited for a
backward direction/M-C jump, with reference to FIG. 137.
Upon receipt of a plural time slots start frame from the M-C [1] as
indicated by an arrow Y73, the S-C [2] (or the SubM-C) generates a
next time slot as indicated by an arrow Y74, based on forward
direction time slots for control and for data operating in the S-C
[2] itself, as indicated by a reference character 137b in a box
137a. That is, the S-C [2] generates: a backward direction time
slot for control or for data designated at a reference numeral
137c; a forward direction jump time slot designated at a reference
numeral 137d; a backward direction jump time slot designated at a
reference numeral 137e; a time slot for upper ring forward
direction time slot for jump designated at a reference numeral
137f; and a time slot for upper ring backward direction time slot
for jump designated at a reference numeral 137g.
Next is described how to generate a backward direction time slot
with reference to FIG. 138.
As explained above with reference to FIG. 137, upon receipt of the
plural time slots start frame from the M-C as indicated by an arrow
Y73, the S-C [2] (or the SubM-C) starts an operation of a time slot
[TS4] which is advanced from a head position of a forward direction
time slot for data by an offset value in accordance with an offset
value (2.times.Dn) described in the plural time slots start frame.
The time slot is herein referred to as a backward direction time
slot.
Next is described how to generate a forward direction jump time
slot with reference to FIG. 139.
Upon receipt of the plural time slots start frame from the M-C [1]
as indicated by an arrow Y73, the S-C [2] (or the SubM-C) starts an
operation of a time slot which is advanced from a head position of
a forward direction time slot for data by an offset value in
accordance with an offset value (Dru) described in the plural time
slots start frame. The time slot is herein referred to as a forward
direction jump time slot.
Next is described how to generate a backward direction jump time
slot with reference to FIG. 140.
Upon receipt of the plural time slots start frame from the M-C [1]
as indicated by an arrow Y73, the S-C [2] (or the SubM-C) starts an
operation of a time slot which is advance from a head position of a
forward direction time slot for data by an offset value, in
accordance with an offset value (2Dn-Dru) described in the plural
time slots start frame. The time slot is herein referred to as a
backward direction jump time slot.
Next is described a first implementation example of a node on a
lower ring (for example, the S-C [5]) with reference to FIG.
141.
The first implementation example is an implementation example of a
lower ring on a multi-ring which performs a unidirectional
communication (an upstream path and a downstream path are
asymmetric). An arrow Y76 indicates ADD/DROP in the lower ring; an
arrow Y77, ADD for an upper ring from a TX1 as a transmission unit;
and an arrow Y78, ADD for upper ring from a TX2.
Different time slots need to operate depending on ADD to a time
slot on the lower ring and ADD to a time slot on the upper
ring.
Units corresponding to the number of time slots of TXs (ADD
interfaces) are thus provided. Wavelengths used in each of the time
slot are designed to be different from each other.
At this time, because different ADD interface are provided for each
time slot, a start timing of a "TS1" of a time t33a illustrating in
a box 141f is advanced by a time corresponding to one round of the
lower ring, to a time t31 as indicated by an arrow Y79. This makes
it possible to perform ADD at different time slots at the same
timing. For example, a simultaneous transmission becomes possible
at a forward direction time slot TS1 [TX1] and a time slot for
upper ring TS3 [TX2]. A receipt also becomes possible at a forward
direction time slot TS1 [RX].
Next is described a second implementation example of a node on the
lower ring (for example, the S-C [5]) with reference to FIG.
142.
The second implementation example is also an implementation example
of a lower ring on a multi-ring which performs a unidirectional
communication (an upstream path and a downstream path are
asymmetric). In the second implementation example, unlike the first
implementation example, an ADD interface is used both for an upper
ring and for a lower ring, as described in a box 142a. This can
reduce device cost because it is not necessary to provide units
corresponding to the number of time slots of the ADD interfaces. An
arrow Y76 indicates DROP in the lower ring; and arrows Y79a and
Y79b, ADD for upper ring from a TX as a transmission unit.
At this time, time slots "TS1 to TS7" which operate at an ADD
interface and are illustrated in a box 142b define time slots at
unequal intervals having a period "t-n".
Herein, let "Pa" and "Pb" be head positions of the earliest and the
last time slots, respectively, of a plurality of time slots in a
period t having the same cycle number. The period t-n is
"Pb-Pa".
At this time, because the number of the ADD interfaces is 1 (one),
it is not possible to simultaneously perform ADD to all the time
slots. Therefore, as illustrated in a box 142c, for example, a time
slot TS1 of [2] TS for upper ring, a time slot TS1 of [1] forward
direction TS, a time slot TS4 of [2] TS for upper ring, and a time
slot TS4 of [1] forward direction TS are transmitted in this order.
This means that a front half TS2a of a time slot TS2 of [2] TS for
upper ring or the like becomes an unavailable area.
Next is described a multi-ring network according to a seventh
embodiment with reference to FIG. 143.
This embodiment describes a multi-ring network (a unidirectional
communication and a bidirectional communication) as illustrated in
FIG. 143, in which time slots in a WDM/TDM network in the
multi-ring network can be exchanged.
In this embodiment, problems of control, in particular, enclosed by
broken lines can be solved.
More specifically, in this embodiment, in a multi-ring network in
which a unidirectional communication takes an upstream path and a
downstream path asymmetric with each other, even if a propagation
delay time for one round on an upper ring is not a multiple integer
of a time slot, the time slot at a time of making one round of the
ring can be synchronized. This is because a propagation delay time
for one round on the ring is measurable. Also, a time slot is
transmitted from the lower ring to the upper ring can be
synchronized. This is because time slot collision at a ring
intersection point node can be prevented.
In this embodiment, in a multi-ring network of a bidirectional
communication, when clockwise and counterclockwise time slots
arrive at the same outputs interface of the same source node, the
two time slots can be synchronized. This is because a time slot can
be set differently depending on a direction of the time slot,
presence or absence of a jump over a ring, presence or absence of a
jump over an M-C, and the like.
Next is described a single ring network to which this embodiment is
directed to, with reference to FIG. 144.
In this embodiment, a single ring network (such a unidirectional
communication and a bidirectional communication) is described, in
which a time slot exchange becomes possible in a WDM/TDM network in
which a single ring network and a plurality of source nodes are
present.
In this embodiment, problems of control, in particular, enclosed by
broken lines can be solved.
More specifically, in this embodiment, in a single ring network in
which a unidirectional communication takes an upstream path and a
downstream path asymmetric with each other, even if a propagation
delay time for one round on an upper ring is not a multiple integer
of a time slot, the time slot at a time of making one round of the
ring can be synchronized. This is because a propagation delay time
for one round on the ring is measurable.
In this embodiment, in a single ring network of a bidirectional
communication, when clockwise and counterclockwise time slots
arrive at the same outputs interface of the same source node, the
two time slots can be synchronized. This is because a time slot can
be set differently depending on a direction of the time slot,
presence or absence of a jump over a ring, and the like.
FIG. 145 is a diagram illustrating a wrap-up of problems in
conventional technologies and specific means for solving the
problems in the present invention.
In this embodiment, the means for solving the problems encircled by
a broken line is distinctively characteristic. Detailed description
of the means for solving the problems including those encircled by
a broken line have been described above and are herein omitted.
As described above, in the seventh embodiment, a source node makes
each of nodes other than the source node have up to two types of
time slots for data, based on a propagation delay time between the
source node and each of nodes other than the source node and based
on a propagation delay time for one round on a ring.
As described above, because each of the nodes other than the source
node has two types of time slots for data, in a multi-ring network,
a time slot for upper ring which is synchronized with a reference
time slot of a ring intersection point node can be arranged at a
node on a lower ring. This achieves such an advantageous effect
that time slot collision at a ring intersection point node can be
prevented.
Further, in arranging a time slot, because a propagation delay time
for one round on a ring is taken into account, even when the
propagation delay time for the ring one round is not an integer
time of a time slot in a single ring network, a source node can
perform an appropriate processing to the time slot arrived. This
achieves such an advantageous effect that a time slot from other
node can be transferred.
DESCRIPTION OF REFERENCE NUMERALS
10 TS information management unit 21 trigger detection unit 22
optical SW control unit 23 transmission control unit 26 control
signal processing unit 50 trigger generation unit 60 TS information
delivery unit 80 TS start delivery unit 81 control signal
generation unit 90 delay time calculation unit 20, 25, 145 TS
synchronization unit 30, 152 optical TS-SW unit 40, 153 TS
transmit-receive unit 101A to 101D optical switch node 120 optical
master node (master node) 121 optical switch node 122 data line
123, 124 control line 31, 141 demultiplexing unit 32, 142
multiplexing unit 133, 143, 143a, 143b control signal reception
unit 134 traffic information collection unit 135 topology
management unit 136 TS (time slot) allocation unit 137 TS start
delivery unit 138 TS information delivery unit 139 time delivery
unit 144 optical TS-SW unit (switch) unit 145 TS synchronization
unit 146 TS transmit-receive unit 147 traffic information
transmission unit 148, 148a, 148b TS information management unit
149, 149b time counter 150 internal clock 311 optical switch unit
312 buffer unit 313 control information transmission unit 314
reference TS synchronization unit 315 delay measurement unit 316
plural TS management unit 317 counter management unit 318 internal
clock unit 319 TS control unit 320 TS amount update timing
calculation unit 321 control information receipt unit 530 ROADM
(Reconfigurable Optical Add/Drop Multiplexer) device 531 optical
fiber network
* * * * *
References